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UNIVERSITY 
CALIFORNIA 


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I.  Q  S. 
REFERENCE  LIBRARY 


A    SERIES    OF    TEXTBOOKS     PREPARED     FOR     THE     STUDENTS     OF    THE 

INTERNATIONAL    CORRESPONDENCE    SCHOOLS    AND    CONTAINING 

IN      PERMANENT      FORM      THE      INSTRUCTION       PAPERS. 

EXAMINATION    QUESTIONS.    AND    KEYS    USED 

IN     THEIR     VARIOUS     COURSES 


PROPERTIES  OF  GASES 

MINE  GASES 

MINE  VENTILATION 

FUELS 


3503C 


SCRANTON 
INTERNATIONAL  TEXTBOOK  COMPANY 


* 


Copyright,  1907,  by  INTBRNATIONAL  TEXTBOOK  COMPANY. 


Entered  at  Stationers'  Hall,  London. 


Properties  of  Gases:  Copyright,  1908,  by  INTERNATIONAL  TEXTBOOK  COMPANY. 
Entered  at  Stationers'  Hall,  London. 

Mine  Gases:  Copyright,  1906,  by  INTERNATIONAL  TEXTBOOK  COMPANY.  Entered 
at  Stationers'  Hall,  London. 

Mine  Ventilation:  Copyright,  1896,  1897,  1900,  by  THE  COLLIERY  ENGINEER  COM- 
PANY. Copyright,  1906,  by  INTERNATIONAL  TEXTBOOK  COMPANY.  Entered  at 
Stationers'  Hall,  London. 

Fuels:  Copyright,  1906.  by  INTERNATIONAL  TEXTBOOK  COMPANY.  Entered  at  Sta- 
tioners' Hall,  London. 

All  rights  reserved. 


PRINTED  IN  THE  UNITED  STATBS. 

lOlbo 


Library 


CONTENTS 


PROPERTIES  OF  GASES 

Physics  of  Gases 5  1 

Definitions 5  1 

Specific  Gravity 5  2 

Determining  Specific  Gravity   ......  5  6 

Heat 5  12 

Measurement  of  Temperature 5  13 

Absolute  Temperature 5  17 

Quantity  of  Heat 5  18 

Sensible  Heat 5  19 

Specific  Heat 5  19 

Latent  Heat 5  23 

Total  Heat 5  24 

Expansion  of  Bodies  by  Heat 5  25 

Atmospheric  Pressure 5  28 

Measurement  of  Atmospheric  Pressure  .    .  5  29 

Volume  and  Pressure  of  Gases 5  34 

Mixture  of  Gases 5  36 

Chemistry  of  Gases 5  38 

Table  of  Molecular  Weights  and  Densities 

of  Mine  Gases 5  47 

The  Atmosphere 5  51 

Combustion 5  54 

Spontaneous  Combustion 5  58 

Physical  Properties  of  Mine  Gases  ....  5  59 

Gob  Fires 5  65 

MINE  GASES 

Occurrence,     Properties,    Behavior,     and 

Detection    of    Mine    Gases 6  1 

Gases  Common  to  Mines 6  1 

iii 


iv  CONTENTS 

MINE  GASES — Continued                                      Section  Page 
Marsh  Gas,  Methane  or  Carbureted  Hydro- 
gen        6  2 

Carbon  Monoxide,  Whitedamp,  or  Carbonic 

Oxide      6  2 

Carbon  Dioxide,  Blackdamp,  or  Carbonic- 
Acid  Gas 6  3 

Hydrogen    Sulphide,   Stinkdamp,  or   Sul- 

pureted  Hydrogen 6  4 

Olefiant  Gas,  Ethene,  or  Ethlyene  ....  6  4 

Nitrous  Oxide 6  5 

Nitrogen 6  5 

Oxygen 6  6 

Hydrogen 6  6 

Mixtures  of  Mines  Gases 6  7 

Firedamp 6  7 

Afterdamp 6  11 

Ignition  of  Gases 6  12 

Effect  of  Coal  Dust 6  22 

Mine  Explosions 6  22 

Gas  Explosion 6  22 

Dust  Explosion 6  23 

Combined  Gas  and  Dust  Explosion     ...  6  25 

Phenomena  of  Explosions 6  26 

Entering  a  Mine  After  an  Explosion  ...  6  30 

Rescue  Work 6  30 

Rescue  Appliances  and  Mine  Supplies  .    .  6  31 

Prevention  of  Explosions 6  33 

Testing  for  Gases  in  Mines 6  35 

Safety  Lamps 6  35 

Special  Lamps      6  47 

Safety-Lamp  Details 6  52 

Oils  for  Safety  Lamps    .    . 6  57 

Relative  Illuminating  Power  of  Oils  ...  6  60 
Relative    Illuminating    Power   of    Safety 

Lamps 6  61 

Testing  for  Gas 6  62 

Gas  Indicators 6  67 


CONTENTS  v 

MINE  GASES — Continued                                      Section  Page 

Safety-Lamp  Houses 6  73 

Portable  Electric  Lamps 6  77 

MINE  VENTILATION 

General  Principles  of  Mine  Ventilation  .    .  13  1 

Production  and  Control  of  Air-Currents    .  13  1 

Form  and  Size  of  Airways 13  9 

>   How  Air-Currents  Are  Produced     ....  13  13 

General  Principles  of  Ventilation    ....  13  16 

Mine  Resistance 13  17 

Air  Measurements .13  25 

To  Measure  the  Velocity  of  Air  in  an  Air- 
way   13  25 

To  Measure  the  Ventilating  Pressure     .    .  13  31 

Calculations  in  Ventilation 13  34 

Practical  Problems 13  39 

Single  Airways  or  Circulations 13  46 

Special  Calculations 13  49 

Comparing  Different  Circulations    ....  13  52 

Power 13  54 

Relation  Between  the  Length  of  an  Air- 
way and  the  Power      13  54 

Relation  Between  Velocity  or  Quantity  of 

Air  to  Power 13  55 

Relation  Between  Area  and  Power     ...  13  55 

General  Power  Ratio 13  56 

Choice  of  Airways 13  65 

Comparing  Similar  Airways 13  67 

Splitting  Air-Currents 14  1 

Air  Splits 14  8 

Calculations  in  Splitting 14  10 

Natural  Splitting 14  10 

Proportionate  Splitting .14  20 

The  Ventilation  of  a  Mine 14  24 

Ventilations  of  Different  Types  of  Mines  .  14  26 

Means  for  Ventilating  Mines 14  37 

Natural  Ventilation                                       ,  14  37 


vi  CONTENTS 

MINE  VENTILATION — Continued                         Section  Page 

Furnace  Ventilation 14  50 

Mechanical  Ventilation 15  1 

Waterfall,  or  Trompe .    .  15  1 

Wind  Cowl .  15  3 

Steam  Jet 15  3 

Ventilating  Fans .15  3 

Disk  Fans 15  4 

Centrifugal  Fans ...  15  5 

Details  of  Fan  Construction 15  7 

Types  of  Centrifugal  Fans .  15  21 

Fan  Designs     15  28 

Fan  Calculations 15  42 

FUELS 

Properties  of  Fuels 16  1 

Combustible  Elements 16  1 

Impurities  in  Fuels 16  3 

Methods  of  Expressing  the  Composition 

of  a  Fuel 16  4 

Solid  Fuels 16  8 

Wood      16  8 

Charcoal 16  11 

Peat  or  Turf      16  12 

Coal 16  13 

Classification  of  Coal 16  14 

Composition  of  Coal 16  18 

Valuation  of  Coal  as  a  Fuel 16  23 

Spontaneous  Ignition  of  Coal 16  32 

Coal  Dust  as  a  Fuel 16  '36 

Pressed  Fuel,  or  Briquets      16  38 

Coke 16  40 

Liquid  Fuels 16  41 

Petroleum      16  41 

Method  of  Burning  Petroleum 16  46 

Gaseous  Fuels 16  52 

Producer  Gas 16  56 

Coal  Gas .16  60 


CONTENTS  vii 

FUELS — Continued                                                 Section  Page 

Water  Gas 16  63 

Uses  of  Gaseous  Fuel 16  67 

Combustion  of  Fuel 16  69 

Heat  of  Combustion 16  85 

Calorific  Value  of  Fuels 16  90 

Analysis  of  Coal  and  Coke 16  91 

Proximate  Analysis 16  91 

Ultimate  Analysis 16  96 

Report  of  Analysis 16  97 

Coal  Hoisting,  Coal  Conveying,  and  Stor- 
ing    16  97 

Self-Filling  Buckets 16  98 

Cranes 16  100 

Conveyers 16  104 

Flight  Conveyers 16  104 

Belt  Conveyers 16  106 

Bucket  Carriers    .    . 16  109 

Chutes 16  115 

Combinations  of  Hoisting  and  Conveying 

Systems 16  117 

Car-Dumping  Machines 16  118 

Brown  Car-Dumping  Machine 16  118 

McMyler  Car-Dumping  Machine 16  120 

Coal  Storage 16  121 


PROPERTIES  OF  GASES 

PHYSICS   OF  GASES 


DEFINITIONS 

1.  Matter  is  the  substance  of  which  all  things  consist. 
It    may    be    defined    as    anything    that    possesses    weight 
or    that    occupies    space.      There    are    three    divisions    of 
matter:    masses,  which    are  bodies  of   matter   appreciable 
to  the  senses;  molecules,  which  are  the  smallest  particles 
of  matter  that  a  body  can  be  divided  into  without  losing  its 
identity;  atoms,   which  are  elementary,  or  chemically  indi- 
visible, portions  of  matter.     Atoms  unite  to  form  molecules 
and  molecules  unite  to  form  masses.     Matter  may  exist  as 
a  solid,  a  liquid,  or  a  gas. 

2.  Natural    Forces. — The     force    that     binds     atoms 
together   to    form    a    molecule    is    a   chemical   force  called 
affinity.     The    force    of    attraction   that    binds    molecules 
together  to  form  mass  is  a  molecular  force  called  cohesion. 
Besides  these  forces  of  attraction,  the  molecules  of  all  matter 
are  acted  on  by  an  opposing  force,  called  repulsion,  which 
tends  to  drive  them  apart.     The  force  of  repulsion,  unlike 
that  of  attraction,  is  not  inherent  in  the  mass,  but  is  an 
induced  or  applied  force  that  is  largely  the  result  of  heat  or 
the  temperature  of  the  body. 

3.  Mass   and  Volume. — The  mass   of    a   body   is   the 
matter  that  it  contains,  and  is  proportional  to  the  weight  of 
the  body;  thus,  a  body  weighing  2  pounds  contains  twice  as 
much  matter  as  a  body  weighing  1  pound.     A  pound  of  cork 

Copyrighted  by  International  Textbook  Company.    Entered  at  Stationers'  Hall,  London 

IB 

145—2 


2  PROPERTIES  OF  GASES  §5 

contains  exactly  the  same  amount  of  matter  as  a  pound  of 
lead.     The  volume  of  a  body  is  the  space  that  it  occupies. 

4.  Density. — Density  is  compactness  of  mass  and  has 
reference  to  the  amount  of  matter  in  a  given  volume.     Thus, 
there  is  more  matter  in  a  cubic  foot  of  iron  than  in  a  cubic 
foot  of  water;    therefore,  we  say  that  iron  is  more  dense 
than  water. 

5.  Weight. — Weight  is  the  result  of  the  attraction  that 
exists  between  the  mass  of  the  earth  and  the  mass  of  any 
other  body.     It  is  because  the  attractive  force  of  the  earth 
is  exerted  equally  on  each  unit  of  mass  that  the  weight  of  a 
body  is  always  proportional  to  its  mass,  at  any  one  place. 


SPECIFIC   GRAVITY 

6.  The  specific  gravity  of  a  body  is  the  ratio  between 
its  weight  and  the  weight  of  an  equal  volume  of  another 
substance  taken  as  a  standard.     The  usual  standard  for  solids 
and  liquids  is  water,  and  its  weight  is  commonly  taken  as 
62.5  pounds  per  cubic  foot,  although  62.425  should  be  used 
when  extreme  accuracy  is  desired. 

Iron  has  a  specific  gravity  of  7.21;  this  means  that  a  given 
volume  of  iron  is  7.21  times  as  heavy  as  an  equal  volume  of 
water;  or,  in  other  words,  iron  contains  7.21  times  as  great 
a  mass. 

Since  gases  are  so  much  lighter  than  water,  it  is  usual  to 
take  the  specific  gravity  of  a  gas  as  the  ratio  between  the 
weight  of  a  certain  volume  of  the  gas  and  the  weight  of  the 
same  volume  of  air  at  the  same  temperature  and  pressure. 

7.  The  specific  gravity  of  any  substance  is  found  by  the 
following  rules: 

Rule  I. — For  solids  or  liquids,  divide  the  weight  of  any  given 
volume  of  the  solid  or  liquid  by  the  weight  of  an  equal  volume  of 
water;  the  quotient  will  be  the  specific  gravity  required. 

Rule  II. — For  gases,  divide  the  weight  of  any  given  volume 
of  the  gas  by  the  weight  of  an  equal  volume  of  air  at  the  same 


§5  PROPERTIES  OF  GASES  3 

pressure   and   temperature;    the   quotient   will   be   the   specific 
gravity  required. 

Or,  expressed  as  a  formula, 

Sp.  Gr.  -  i 

in  which   w  —  weight  of  any  given  volume  of  substance; 
W  =  weight  of  an  equal  volume  of  standard. 

EXAMPLE. — If  the  weight  of  a  cubic  foot  of  mercury  is  taken  as 
850  pounds  at  32°  F.,  what  is  its  specific  gravity  at  this  temperature, 
taking  the  weight  of  a  cubic  foot  of  water  at  62.5  pounds? 

SOLUTION. — Substituting  the  given  values  in  the  formula, 


8.  The  practical  application  of  specific  gravity  in  mining 
is  to  determine  thereby  the  weight  of  a  given  body  or  sub- 
stance when  its  volume  is  known.  For  this  purpose,  the 
rules  given  in  Art.  7  are  reversed,  making  them  read  as 
follows: 

Rule  I. — For  liquids  or  solids,  multiply  the  weight  of  any 
given  volume  of  water  by  the  specific  gravity  of  the  solid  or 
liquid;  the  product  will  be  the  weight  of  an  equal  volume  of 
such  solid  or  liquid. 

Rule  II. — For  gases,  multiply  the  weight  of  a  cubic  foot  of 
air  at  the  given  temperature  and  pressure  by  the  specific  gravity 
of  the  gas;  the  product  will  be  the  weight  of  an  equal  volume  of 
the  gas  at  the  same  temperature  and  pressure. 

Or,  expressed  as  a  formula, 

w  =   IV  x  Sp.  Gr. 
in  which  the  quantities  have  the  meanings  given  in  Art.  7. 

EXAMPLE  1.— Find  the  weight  of  a  cubic  foot  of  anthracite  having 
a  specific  gravity  of  1.5. 

SOLUTION. — Substituting  the  given  values  in  the  formula, 
w  =  62.5  X  1.5  =  93.75  Ib.     Ans 

EXAMPLE  2.— Find  the  weight  of  1  cubic  foot  of  carbon  dioxide 
(carbonic-acid  gas)  having  a  specific  gravity  of  1.5291  at  60°  F.  and 


PROPERTIES  OF  GASES 


§5 


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Substance 

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Powder,  separate 
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§5 


PROPERTIES  OF  GASES 


29.925  inches  barometric  pressure  (sea  level),  assuming  the  weight  of 
a  cubic  foot  of  air,  at  this  temperature  and  pressure,  as  .07638  pound. 
SOLUTION. — Substituting  the  given  values  in  the  formula, 
w  =  .07638  X  1.5291  =  .11679  Ib.     Ans. 

9.  Table  I  gives  the  specific  gravities  and  weights  per 
cubic  foot  of  some  of  the  solids  and  liquids  important  in 
mining.  In  calculating  the  weight  per  cubic  foot,  the  weight 
of  1  cubic  foot  of  water  is  taken  as  62.5  pounds.  Table  II 
gives  the  specific  gravities  of  the  common  mine  gases,  air 
of  the  same  temperature  and  pressure  being  taken  as  the 
standard. 

TABLE   II 


Gas 

Specific 
Gravity 

Air      ...                    ... 

l.OOO 

Hydrogen  H    

.o6cH 

Oxygen  O     

I.IO57 

Nitrogen  N      .    .        .    . 

.0714 

Carbureted  hydrogen!  „ 
Methane  (marsh  gas)/ 
Ethylene  (olefiant  gas)  C^ff*    
Carbon  monoxide  (carbonic  oxide)  CO     .    .    . 
Carbon  dioxide  (carbonic  acid)  CO  
Hydrogen  sulphide  J^tS 

•5590 

.9700 
.9670 
1.5291 
I   1912 

EXAMPLES    FOR    PRACTICE 

1.  What  is  the  weight  of  a  cubic  foot  of  anthracite,  having  a  specific 
gravity  of  1.55?  Ans.  96.875  Ib. 

2.  Find  the  weight  of  100  cubic  yards  of  earth,  having  a  specific 
gravity  of  1.4.  Ans.  118.125  T. 

3.  What  is  the  weight  of  200  cubic  feet  of  carbon  dioxide,  at  60°  F., 
and   barometer  at  30  inches,    the  specific  gravity  of    the  gas    being 
1.5291?     Weight  of  1  cubic  foot  of  air  at  this  temperature  and  pressure 
is  .0766  pound.  Ans.  23.4258  Ib. 

4.  Find  the  weight  of  500  cubic  feet  of  marsh  gas  at  a  temperature 
of  60°  F.,  and  a  pressure  due  to  30  inches  of  barometer,  the  gas  having 
a  specific  gravity  of  .559.  Ans.  21.41  Ib.  (nearly) 


PROPERTIES  OF  GASES 


DETERMINING    SPECIFIC    GRAVITY 

10.  The  specific  gravity   of  solids  and  liquids  may  be 
determined  by  balances,  by  hydrometers,  and  by  specific- 
gravity  bottles. 

11.  Determination  of  the  Specific  Gravity  of  Solids 
by  a  Balance. — The  principle  on  which  the  determination  of 
the  specific  gravity  of  solids  depends  is  that  a  body  entirely 
submerged  in  any  liquid  is  buoyed  up  by  a  force  exactly 
equal  to  the  weight  of  the  volume  of  the  liquid  displaced, 

and  the  volume  of  the 
liquid  displaced  is  equal 
to  the  volume  of  the 
submerged  body. 

This  principle  is 
applied  as  follows: 
Weigh  the  body  first  in 
the  air,  then  in  water, 
suspending  it  by  a 
string  attached  to  a 
scale  pan,  as  shown  in 
Fig.  1.  The  difference 
between  the  two  weights 
will  be  the  weight  of  an 
equal  volume  of  water. 
The  ratio  of  the  weight 
in  air  to  the  difference  thus  found  will  be  the  specific  gravity. 
Let  W  =  weight  of  substance  in  air; 

w  =  weight  of  substance  in  water; 
W—   w  =  weight  of  displaced  water. 
W 


Then, 


Sp.  Gr.  = 


W-w 


12.  If  the  body  is  lighter  than  water,  attach  to  it  a  piece  of 
iron  or  other  substance  sufficiently  heavy  to  sink  both.  Then 
weigh  both  bodies  in  air  and  both  in  water.  Weigh  each  sepa- 
rately in  air  and  weigh  the  iron  in  water.  Subtract  the  weight 
of  the  two  bodies  in  water  from  their  weight  in  air,  and  the 


§5  PROPERTIES  OF  GASES  7 

result  will  be  the  weight  of  a  volume  of  water  equal  to  the  vol- 
ume of  the  two  bodies.  Find  the  difference  of  the  weights  of 
the  iron  in  air  and  in  water;  this  will  be  the  weight  of  a  vol- 
ume of  water  equal  to  the  volume  of  the  iron.  Subtract  this 
result  from  the  weight  of  the  volume  of  water  equal  to  the 
volume  of  the  two  bodies,  and  the  result  will  be  the  weight  of 
a  volume  of  water  equal  to  the  volume  of  the  light  body.  The 
weight  of  the  light  body  in  air  divided  by  the  weight  of  its 
equal  volume  of  water  is  the  specific  gravity  of  the  light  body. 
Let  W  =  weight  of  both  bodies  in  air; 

W  =  weight  of  both  bodies  in  water; 

w    =  weight  of  light  body  in  air; 

Wi  =  weight  of  heavy  body  in  air; 

IV,  =  weight  of  heavy  body  in  water. 
Then,  the  specific  gravity  of  the  light  body  is  given  by 

Sp<  Gr'  =  (w-  w)  -(w,-  w,} 

13.  Determination  of  Specific  Gravity  of  Solids  by 
a  Specific-Gravity  Bottle  and  Balance. — In  this  method, 
a  bottle,  Fig.  2,  having  a  tightly 
fitting  stopper  perforated  by  a 
small  glass  tube  is  used.  The  sub- 
stance whose  specific  gravity  is  to 
be  determined  must  be  insoluble 
in  water  and  in  the  condition  of 
small  grains  or  powder.  It  is  first 
weighed;  the  bottle  is  then  weighed 
filled  with  water;  and  finally,  the 
weighed  substance  is  introduced 
into  the  bottle,  displacing  an 
amount  of  water  equal  to  its  own 
volume  or  bulk,  and  the  bottle 
again  weighed.  Each  time  before 
weighing,  the  bottle  is  carefully  FIG.  2 

filled  to  the  top  of  the  small  tube,  all  excess  of  water  being 
removed  with  a  small  piece  of  blotting  paper.  In  this  case 
the  following  formula  is  used: 


8  PROPERTIES  OF  GASES  §5 

Let    W  =  weight  of  substance; 

Wt.  =  weight  of  bottle  filled  with  water; 

•w,  =  weight  of  bottle,  water,  and  substance. 

Then,  Sp.  Gr.  =  - 

W  +  w,  —  W* 

14.  The  specific  gravity  of  any  substance  soluble  in  water 
may  be  determined  with  the  specific-gravity  bottle,  by  using 
instead  of  the  water  any  liquid  in  which  the  substance  is 
insoluble.  This  will  give  its  specific  gravity  referred  to  such 
liquid.  Afterwards,  the  specific  gravity  of  the  liquid,  referred 
to  water,  is  determined,  as  already  explained,  and  the  spe- 
cific gravity  of  the  substance  as  first  obtained  is  multiplied 

by  the  specific  gravity  of   the  liquid   employed. 

The  result  will  be   the   specific   gravity   of  the 

substance. 

15.  Determining  Specific  Gravity  of 
Liquids  by  Balance. — There  are  two  methods 
of  determining  the  specific  gravity  of  liquids  by 
means  of  the  balance.  The  simpler  and  better 
method  is  to  weigh  out  equal  volumes  of  the 
liquid  and  water,  and  the  most  accurate  way  to 
do  this  is  to  weigh  them  in  succession  in  the 
same  vessel,  taking  care  to  have  it  equally  full  on 
FIG.  s  both  occasions.  The  vessel  shown  in  Fig.  3  is 
convenient  when  small  quantities  are  to  be  weighed.  It  is 
easily  made  by  blowing  a  bulb  on  a  glass  tube.  On  that 
portion  of  the  tube  that  is  narrowed  by  being  drawn  out 
over  a  flame,  a  scratch  is  made  with  a  file.  The  bulb,  after 
being  filled  up  to  the  scratch  with  the  liquid,  is  weighed, 
emptied,  cleaned,  dried,  filled  with  water,  and  weighed 
again.  Care  should  be  taken  that  both  liquids  have  the 
same  temperature.  This  is  easily  accomplished  by  immers- 
ing the  bulb  filled  with  liquid  for  some  time  in  water,  part 
of  which  is  later  used  in  the  second  weighing.  In  this  case, 
Let  w  =  weight  of  bulb  empty; 

W^  =  weight  of  bulb  filled  with  water; 
Wt  =  weight  of  bulb  filled  with  liquid. 


§5 


PROPERTIES  OF  GASES 


Then, 


Sp.  Gr.  = 


W,-w 


16.  The  other  method  consists  of  three  operations,  as 
follows:  A  small  solid  substance,  as  a  coin  or  other  piece 
of  metal,  is  weighed  successively  in  air,  in  water,  and  in  the 
liquid  whose  specific  gravity  is  to  be  determined.  In  this 
case, 

Let        W  =  weight  of  substance  in  air; 

Wi  =  weight  of  substance  in  water; 
w,  =  weight  of  substance  in  the  liquid. 

It  will  be  readily  observed  that  W  —  w*  equals  the  weight 
of  a  certain  volume  of  the  liquid  whose  specific  gravity  is 


FIG.  4 


to  be  determined,  and  W  —  w,.  equals  the  weight  of  an  equal 
volume  of  water. 


Then, 


Sp.  Gr.  = 


-  w, 


W-w, 


17.  Determining  Specific  Gravity  by  the  Hydrom- 
eter.— There  are  two  types  of  the  hydrometer  employed — 
Nicholson's  constant  immersion  hydrometer  and  Beaum^'s 
variable  immersion   hydrometer.     Different   forms  of  each 
type  are  in  use. 

18.  Nicholson's  hydrometer,  Fig.  4,  for  determining 
the  specific  gravity  of  insoluble  solids  consists  of  a  hollow 


10  PROPERTIES  OF  GASES  §5 

cylinder  carrying  at  its  lower  end  a  basket  d  heavy  enough 
to  keep  the  apparatus  upright  when  placed  in  water.  At  the 
top  of  the  cylinder  is  a  vertical  rod  to  which  is  attached  a 
shallow  pan  a  for  holding  the  weights,  etc.  The  cylinder 
is  of  such  a  size  and  buoyancy  that  a  certain  weight  W  must 
be  placed  on  the  pan  to  sink  it  to  a  given  point  c  on  the  rod. 
The  body  whose  specific  gravity  it  is  desired  to  find,  is  placed 
in  the  pan  a  and  enough  weight  w  is  added  to  sink  the  point  c 
to  the  water  level.  It  is  evident  that  the  weight  of  the  given 
body  is  W  —  w.  The  body  is  now  removed  from  the  pan  a 
to  the  basket  d,  and  an  additional  weight  is  added  to  the  pan 
to  sink  the  point  c  to  the  water  level.  Represent  the  weight 
now  in  the  pan  by  W.  The  difference  W  —  w  is  the  weight 
of  a  volume  of  water  equal  to  the  volume  of  the  body. 

Hence,  Sp.  Gr.  =  ^-~  w 


EXAMPLE.  —  The  weight  necessary  to  sink  the  hydrometer  to  the 
point  c  is  16  ounces;  the  weight  necessary  when  the  body  is  in  the 
pan  a  is  7.3  ounces,  and  when  the  body  is  in  the  basket  d,  10  ounces; 
what  is  the  specific  gravity  of  the  body? 

SOLUTION.—  Substituting  in  the  formula, 


19.  To  obtain  the  specific  gravity  of  any  liquid  with  this 
hydrometer,  it  is  floated  in  the  liquid  whose  specific  gravity 
is  to  be  obtained,  and  a  sufficient  number  of  weights  are 
placed  in  the  scale  pan  to  sink  it  to  the  standard  mark, 
giving  the  following  results: 

Sp.  Gr.  = 


in  which  W  =  weight  of  hydrometer; 

wt  =  weights  required  to  sink  hydrometer  in  water; 
wt  =  weights  required  to  sink  hydrometer  in  the 

liquid. 

It  will  be  readily  observed  that  W  +  w^  and  W  +  wt  are 
the  buoyant  pressures,  or  the  exact  weights,  of  like  volumes 
of  the  water  and  the  liquid,  respectively,  displaced  by  the 
hydrometer.  The  liquid  may  be  heavier  or  lighter  than 


§5  PROPERTIES  OF  GASES  11 

water.  If  but  a  small  amount  of  the  liquid  whose  specific 
gravity  is  to  be  determined  is  at  hand,  its  specific  gravity 
may  be  found  by  placing  1  cubic  centimeter  (.061  cubic  inch) 
of  the  liquid  in  a  small  vial  that  has  been  balanced  in  the 
scale  pan  of  the  hydrometer  to  determine  its  weight.  The 
weights  required  to  sink  the  hydrometer  with  the  vial  and 
liquid,  when  subtracted  from  the  weight  required  to  sink  it 
with  the  vial  alone,  will  give  the  weight  of  1  cubic  centimeter 
of  the  liquid;  and  the  specific  gravity  of  the  liquid  is  then 
obtained  by  dividing  this  weight  by  the  weight  of  1  cubic 
centimeter  of  water  (1  gram  =  15.432  grains).  In  these  deter- 
minations, the  hydrometer  takes  the  place  of 
the  balance. 

20.  Beaume's  hydrometer,    Fig.    5,    con- 
sists of  a  glass  tube,  near  the  bottom  of  which 
are  two  bulbs.     The  lower  and   smaller  bulb  is 
loaded   with   mercury   or   shot,  so    as    to  cause 
the    instrument  to  remain  in  a  vertical  position 
when  placed  in  the  liquid.     The  upper  bulb  is 
filled  with  air,  and  its  volume  is  such  that  the 
whole    instrument     is     lighter     than    an    equal 
volume    of    water.     The    point    to     which    the 
hydrometer  sinks  when  placed  in  water  is  usu-         Plo<  5 
ally  marked,  the  tube  being  graduated  above  and  below  in 
such  a  manner  that  the   specific   gravity  of  the  liquid  can 
be  read  directly.     It  is  customary  to  have  two  instruments: 
one  with  the  zero  point  near  the  top  of  the  stem,  for  use 
in  liquids  heavier  than  water;   and  the  other  with  the  zero 
point  near  the  bulb,  for  use  in  liquids  lighter  than  water. 

21.  Determining   the    Specific   Gravity  of   Gases. 

The  determining  of  the  specific  gravity  of  gases  requires 
such  delicate  apparatus  and  skill  that  it  cannot  be  done 
except  by  an  experienced  person  in  a  well-equipped  labora- 
tory. The  method  of  calculating  the  specific  gravity  of  a 
gas  from  its  chemical  composition  is  explained  in  Art.  93. 


12          PROPERTIES  QF  GASES          §5 

HEAT 

22.  Heat  is  a  form  of  energy,  and  is  conceived  to  be  a 
motion,  or  vibration,  of  the  molecules  composing  matter. 
It   is    this   movement   of   the  molecules    that   is    generally 
believed    to    cause    the    sensation    of    warmth.       Another 
effect  of   this    motion   is   to  cause  the  molecules    to    sepa- 
rate  farther  apart  and  cause  a  body  to  expand  in  volume. 
The  hotter  the  body  becomes,  the  more  rapid  become  the 
vibrations  of  its  constituent  molecules  and  the  greater  the 
expansion. 

23.  Forms    of    Matter. — There    are    three    forms    of 
matter — solid,  liquid,  and  gaseous.     The  form  of  matter  is 
determined  by  the  freedom  of  its  molecules;  in  solids,  the 
molecules   are  more   or  less  rigid  and  fixed;    in  liquids, 
the  molecules  move  freely  among  one  another;    in  gases, 
the    freedom    of   the    motion    of   the   molecules    is    greatly 
increased  and  cohesion  is  entirely  overcome.     The  form  of 
matter  is  closely  associated  with  the  amount  of  heat  that 
the  substance  contains.     Many  kinds  of  matter  assume  dif- 
ferent forms  under  different  conditions  of  heat  and  pressure; 
for  example,  water  exists  as  a  solid  (ice),  a  liquid  (water), 
or  a  gas  (steam).     The  air  that  we  breathe  as  a  gas  has 
been  changed  to  a  liquid  and  even  to  a  solid  under  certain 
conditions  of  temperature  and  pressure.     The  natural  form 
of  any  kind  of  matter  is  that  form  in  which  it  exists  under 
natural  conditions.     Most  kinds  of  matter  have  but  one  nat- 
ural form,  and  require  the  application  of  heat,  or  of  pressure 
and  cold,  to  cause  them  to  exist  in  any  other  form.     Mercury 
exists   naturally  as  a  liquid,   but   at   a    lower   temperature 
( —  39°F.)  is  frozen,  or  converted  into  a  solid,  and  at  a  higher 
temperature  (675°F.)  is  vaporized,  or  converted  into  a  gas. 
In    all    these    cases    the    identity    of    the    matter    remains 
unchanged — the  mercury  is  mercury  whether  existing  as  a 
solid,  a  liquid,  or  a  gas.     In  other  words,  the  change  of 
form  is  not  caused  by  a  chemical  change  in  the  molecules  of 
the  matter;  they  do  not  form  another  substance. 


§5  PROPERTIES  OF  GASES  13 

24.  Sources  of   Heat. — Heat  is  produced  in  various 
ways:  by  friction,  by  percussion,  by  chemical  action.     In  all 
these  cases,  heat  is  the  result  of  the  vibration  of  the  mole- 
cules of  matter.     Other  sources  of  heat  are  the  sun's  rays, 
the  heat  of  the  earth,  animal  heat;  heat  is  always  produced 
where  'combustion  takes  place,   and   is    sometimes    accom- 
panied with  light  and  flame. 

25.  Transmission    of    Heat. — Heat    is    transmitted, 
according  to  conditions,  by  radiation,  by  conduction,  and  by 
convection.     Radiated  heat  is  that  portion  of  the  heat  of  a 
body  which  passes  into  the  surrounding  air  or  other  medium; 
the  body  is  then  said  to  lose  heat  by  radiation.     The  heat 
of  a  stove  is  radiated  to  an  object  near  it. 

Conduction  refers  to  the  travel  of  heat  from  one  portion 
of  a  solid  body  to  another;  or  the  heat  may  pass  from  one 
body  to  another  with  which  it  is  in  contact.  When  one  end 
of  an  iron  rod  is  heated,  the  heat  travels  to  the  other  end  by 
conduction. 

Convection  takes  place  only  in  fluids  (liquids  or  gases),  and 
refers  to  the  carrying  of  heat  from  one  place  to  another  by 
the  circulation  of  the  fluid.  Convection  is  best  illustrated  by 
the  circulation  in  a  steam  boiler,  where  the  water,  heated 
by  contact  with  the  crown  sheets  over  the  fire,  rises  and  cir- 
culates, carrying  its  heat  to  cooler  portions  of  the  boiler. 


MEASUREMENT  OF  TEMPERATURE 

26.  Temperature  is  a  term  used  to  express  the  intensity 
of  heat,  or  the  rapidity  of  vibration  of  the  molecules.  A  hot 
body  is  said  to  have  a  high  temperature;  and  a  cold  body,  a  low 
temperature.  The  most  common  measure  for  temperature  is 
the  sensation  of  warmth  that  it  produces.  According  to  the 
character  of  this  sensation,  a  body  is  cold,  warm,  or  hot. 
For  scientific  purposes,  however,  the  sense  of  feeling  is 
not  a  sufficiently  accurate  method  for  measuring  tempera- 
tures; accordingly,  temperature  is  measured  by  certain  of  the 
effects  produced  by  heat.  For  all  ordinary  temperatures,  the 
most  convenient  effect  to  note  is,  that  most  bodies  expand 


14 


PROPERTIES  OF  GASES 


§5 


with  a  rise  of  temperature.  For  general  purposes  of  tem- 
perature measurement,  mercury  and  alcohol  are  the  most  con- 
venient substances  to  use — the  former  because  it  boils  only  at 
a  very  high  temperature,  and  the  latter  because  it  does  not 
solidify  at  the  lowest  temperature  produced  by  ordinary 

means.  For  ordinary 
mine  use,  the  mer- 
curial thermometer 
serves  every  pur- 
pose and  is  the  one 
commonly  used. 

27.     The    Ther- 
mometer. —  The 

thermometer,  Fig.  6, 
consists  of  a  capillary 
glass  tube  with  a 
bulb  at  one  end. 
The  bulb  and  a  por- 
tion of  the  tube  are 
filled  with  the  liquid 
to  be  used.  The 
liquid  is  then  boiled 
to  expel  the  air,  and 
the  tube  is  sealed  at 
the  top,  so  that  the 
upper  part  of  it  is  a 
vacuum  except  for  a 
small  quantity  of 
vapor  due  to  the 
FlG-6  evaporation  of  the 

liquid  used.     The  tube  is  attached  to  a  base  on  which  is 

marked  the  scale. 

28.  Thermometer  Scales. — Fig.  6  shows  a  mercurial 
thermometer  with  two  sets  of  graduations.  The  one  on  the 
left,  marked  /%  is  the  Fahrenheit  scale  commonly  used  in  the 
United  States  and  in  England;  the  one  on  the  right,  marked  C, 
is  the  Celsius,  or  centigrade,  scale,  and  is  used  throughout 


§5  PROPERTIES  OF  GASES  15 

the  world  for  scientific  work,  on  account  of  the  graduations 
being  better  adapted  for  calculation.  Another  scale,  the 
Reaumur,  is  largely  used  in  Germany  and  Russia.  In 
graduating  thermometers,  two  fixed  points,  the  melting  point 
of  ice  (or  the  freezing  point  of  water)  and  the  boiling  point 
of  water  at  sea  level,  are  determined.  In  the  Fahrenheit 
scale,  the  melting  point  of  ice  is  marked  32°  and  the  boiling 
point  of  water  212°;  in  the  centigrade  scale,  the  melting  point 
of  *ice  is  marked  0°,  or  zero,  and  the  boiling  point  of  water 
100°;  in  the  Reaumur  scale,  the  melting  point  of  ice  is  marked 
0°  and  the  boiling  point  of  water  80°.  The  graduation  of 
each  of  these  scales  is  continued  above  the  boiling  point  and 
below  the  freezing  point.  On  the  Fahrenheit  scale,  0°  is  32° 
below  the  freezing  point.  Below  the  zero  point  on  each 
scale,  the  readings  are  negative  and  are  preceded  by  a  minus 
(-)sign;  thus,  -10°  means  10°  below  0°.  All  readings 
above  0°  are  positive,  but  the  plus  sign  ( + )  is  omitted. 

It  will  be  seen  that  180°  on  the  Fahrenheit  scale  covers 
the  same  range  in  temperature  as  100°  on  the  centigrade 
scale  and  as  80°  on  the  Reaumur  scale.  In  expressing  a 
temperature,  the  letters  F.,  C.,  or  R.  placed  after  the  figures 
indicate  whether  the  temperature  is  expressed  in  the  Fahren- 
heit, centigrade,  or  Reaumur  scale,  respectively. 

29.  It  is  often  necessary  to  express  a  temperature  given 
in  one  scale  in  terms  of  another. 

To  change  centigrade  temperatures  into  their  correspond- 
ing Fahrenheit  values: 

Rule  I. — Multiply  the  temperature,  centigrade,  by  •£  and  add 
32°;  the  result  will  be  the  temperature,  Fahrenheit. 

To  change  Fahrenheit  temperatures  into  their  correspond- 
ing centigrade  values: 

Rule  II. — Subtract  32°  from  the  temperature,  Fahrenheit, 
multiply  by  f,  and  the  result  will  be  the  temperature,  centigrade. 

To  change  Reaumur  temperatures  to  their  corresponding 
Fahrenheit  values: 


16  PROPERTIES  OF  GASES  §5 

Rule  III. — Multiply  the  temperature,  Reaumur,  by  f  and 
add  32°;  the  result  will  be  the  temperature,  Fahrenheit. 

To  change  Fahrenheit  temperatures  to  their  corresponding 
Reaumur  values: 

Rule  IV. — Subtract  32°  from  the  temperature,  Fahrenheit, 
multiply  by  9,  and  the  result  will  be  the  temperature,  Reaumur. 

To  change  Reaumur  temperatures  into  their  corresponding 
centigrade  values: 

Rule  V. — Multiply  the  temperature,  Rtaumur,  by  i,  and 
the  result  will  be  the  temperature,  centigrade. 

To  change  centigrade  temperatures  into  their  correspond- 
ing Reaumur  values: 

Rule  VI. — Multiply  the  temperature,  centigrade,  by  i,  and 
the  result  will  be  the  temperature,  Reaumur. 

Expressing  these  rules  by  means  of  formulas, 
Let  tc  =  temperature  centigrade; 

//  =  temperature  Fahrenheit; 
tr  =  temperature  Reaumur. 
Then,  /,  =  •£/, +  32°  (1) 

tc  =  •§•(/,-  32°)        (2) 

/,=  */, +  32°  (3) 

/„=*('/ -32°)        (4) 

/.  =  */,  (5) 

/,=  U  (6) 

30.  In  using  the  above  formulas,  the  sign  must  always 
be  considered  as  indicating  whether  the  temperature  is 
above  or  below  0°. 

EXAMPLE  1. — Convert  50°  C.  into  the  corresponding  Fahrenheit 
reading, 

SOLUTION.— Using  formula  1,  Art.  29, 

/,  =  f  x  50  +  32  =  122°  F.     Ans. 

EXAMPLE  2.— Convert  -10°  C.  into  the  corresponding  Fahrenheit 
reading. 

SOLUTION.— Using  formula  1,  Art.  29, 

/,  =  (|  x  -10)  +  32  =  -18  +  32  =  14°  F.    Ans. 


§5  PROPERTIES  OF  GASES  17 

EXAMPLE  3. — Convert  —30°  C.  into  the  corresponding  Fahrenheit 
reading. 

SOLUTION. — Using  formula  1,  Art.  29, 

/,  =  (|  x  -30)  +  32  =  -54  +  32  =  -22°  F.     Ans. 

EXAMPLE  4. — Convert  -4°  F.  into  the  corresponding  centigrade 
reading. 

SOLUTION. — Using  formula  2,  Art.  29, 

tt  =  |  (-4  -  32)  =  \  X  -36  =  -20°  C.     Ans. 

31.  It  will  be'noticed  that  in  these  formulas  32  is  added 
and  subtracted  algebraically;  that  is,  when  the  signs  are  like, 
the  quantities  are  added  together,  their  sum  having  the  same 
sign;  but,  when  the  signs  are  unlike,  the  lesser  quantity  is 
subtracted  from  the  greater;  and  the  remainder  takes  the  sign 
of  the  greater.  Thus,  in  example  2,  where  +32  is  added 
to  —18,  subtract  18  from  32,  and  the  remainder,  14,  takes 
the  plus  sign.  In  example  3,  subtract  32  from  54,  and  the 
remainder,  22,  takes  the  minus  sign. 


EXAMPLES    FOR    PRACTICE 

1.  What  temperature  Fahrenheit  corresponds  to  100°  C.? 

Ans.  212°  F. 

2.  Convert  290°  C.  into  the  corresponding  Fahrenheit  reading. 

Ans.  554°  F. 

3.  What  reading  on  the  centigrade  scale  corresponds  to  5°  F.? 

Ans.  -15°  C. 

4.  Convert  —40°  F.  into  the  corresponding  centigrade  reading. 

Ans.  -40°  C. 

32.  Absolute  Temperature. — From  experiments  and 
mathematical  calculations,  it  has  been  concluded  that  at  460° 
below  zero  on  the  Fahrenheit  scale,  or  273°  below  zero  on 
the  centigrade  scale,  all  molecular  vibrations  cease.     This 
point  is  called  absolute  zero.     Absolute  temperature  is  the  tem- 
perature measured  from  the  absolute  zero. 

33.  For  converting  ordinary  temperatures  to  absolute 
temperatures  use  the  following  rules: 

For  the  Fahrenheit  scale: 

Rule  I. — Add  460°  to  the  Fahrenheit  thermometer  reading, 
and  the  result  will  be  the  absolute  temperature,  Fahrenheit. 


18  PROPERTIES  OF  GASES  §5 

For  the  centigrade  scale: 

Rule  II. — Add  273°  to  the  centigrade  thermometer  reading^ 
and  the  result  will  be  the  absolute  temperature,  centigrade. 

Expressed  by  formulas,  these  rules  for  finding  the  abso- 
lute temperature  are  as  follows: 
For  the  Fahrenheit  scale: 

7>=460  +  /,          (1) 

in  which  Tf  =  absolute  temperature  (F.); 

//  =  ordinary  temperature  (F.). 
For  the  centigrade  scale: 

Tt  =  273°  +  /,         (2) 

in  which  Tc  =  absolute  temperature  (C.); 

te   =  ordinary  temperature  (C.). 

NOTE. — Unless  otherwise  stated,   T  signifies  absolute  temperature 
and  t  ordinary  temperature. 


QUANTITY    OF    HEAT 

34.  The  quantity  of  heat  in  a  body  is  quite  different 
from  its  temperature.     A  pail  of  water  and  a  barrel  of  water 
may  be  of   the  same  temperature,  yet  it  is  plain  that  the 
barrel  of  water  contains  the  greater  quantity  of  heat.     The 
quantity  of  heat  in  a  body  is  expressed  in  heat  units. 

35.  Heat  Units.  —The  British  thermal  unit  (abbre- 
viated to  B.  T.  U.)  is  the  heat  unit  most  commonly  used  in  the 
United  States  and  England,  and  is  the  quantity  of  heat  that 
will  raise  the  temperature  of  1  pound  of  water  at  its  maxi- 
mum density  (39.1°  F.)  through  1°  F. 

The  French  calorie  is  a  heat  unit  based  on  the  metric 
system,  and  is  the  amount  of  heat  necessary  to  raise  1  kilo- 
gram of  water  1°  C.  at  4°  C.  It  is  equal  to  3.968  B.  T.  U. 

The  pound  calorie,  which  is  also  largely  used,  is  the 
amount  of  heat  required  to  raise  the  temperature  of  1  pound 
of  water  1°  C.;  it  is  equal  to  1.8  B.  T.  U. 

36.  Mechanical  Equivalent  of  Heat. — Since  one  form 
of  energy  can  be  converted  into  another,  heat  can  be  con- 
verted into  mechanical  energy,  and,  conversely,  mechanical 


§5  PROPERTIES  OF  GASES  19 

energy  can  be  converted  into  heat.  There  is  a  definite  rela- 
tion between  heat  energy  and  mechanical  energy.  It  has 
been  found,  by  experiment,  that  778  foot-pounds  of  work  is 
required  to  produce  1  B.  T.  U.,  and,  conversely,  the  expendi- 
ture of  1  B.  T.  U.  produces  778  foot-pounds  of  work.  The 
knowledge  of  this  fact  enables  us  to  calculate  the  theoretical 
work  that  may  be  performed  by  the  energy  stored  in  1  pound 
of  coal.  For  example,  if  the  heating  value  of  1  pound  of 
bituminous  coal  is  14,400  B.  T.  U.,  and  if,  as  experiment  has 
shown,  1  B.  T.  U.  will  develop  778  foot-pounds  of  work, 
the  work  stored  in  1  pound  of  bituminous  coal  is  778  X  14,400 
=  11,203,200  foot-pounds.  This  means  that  the  energy 
stored  in  1  pound  of  coal,  if  totally  utilized,  would  raise  a 
weight  of  over  5,000  tons  through  a  vertical  height  of  1  foot. 
Only  a  very  small  percentage  of  this  total  stored  energy  of 
the  coal,  however,  is  realized  in  a  steam  engine,  for  with 
good  coal  and  a  good  boiler  only  from  4  to  5  per  cent,  of 
the  stored  energy  can  be  converted  into  useful  work. 

37.  Sensible   Heat. — If   a  certain   amount  of   heat  is 
absorbed  by  a  substance,  a  portion  of  this  heat  is  utilized 
in  changing  the  temperature  of  the  substance;  this  portion  is 
known  as  sensible  heat.     The  temperature  of  a  substance 
considered  alone  does  not   measure    the   quantity  of   heat 
absorbed,   since   all  matter  has  not  the   same  capacity  for 
heat.     Different  substances  acted  on  by  the  same  amount  of 
heat  for  an  equal  length  of    time  do  not  attain  the  same 
temperature.     The  quantity  of  heat  absorbed  by  any  sub- 
stance, for  a  given  rise  of  temperature,  when  there  is  no 
change  in  the  state  of  the  substance,  is  in  proportion  to  the 
weight  of  matter  heated  and  its  capacity  to  absorb  heat,  that 
is,  its  specific  heat. 

38.  Specific  Heat. — The  specific  heat  of  a  substance  is 
the  ratio  between  the  quantity  of  heat  required  to  raise  the 
temperature  of  equal  weights  of  that  substance  and  water  at 
maximum    density  through   an    equal   number  of   degrees. 
The  specific  heat  of  any  substance,  referred  to  water  as  unity, 
expresses,  therefore,  the  number  of  B.  T.  U.  required  to  raise 


20  PROPERTIES  OF  GASES  §5 

the  temperature  of  1  pound  of  that  substance  through  1°  F. 
The  specific  heat  of  a  solid  is  referred  to  water  as  a  standard; 
the  specific  heat  of  a  gas  may  be  referred  to  either  water  or  air. 

39.  Suppose  that  two  iron  balls  of  the  same  weight  are 
heated  to  a  temperature  of   212°   F.     Being  of  the   same 
weight,  they  possess  the  same  quantity  of  heat.     Plunge  one 
of  the  balls  into  a  vessel  containing  10  pounds  of  water  and 
the  other  into  a  vessel  containing  10  pounds  of  mercury,  both 
mercury  and  water  being  at  a  temperature  of  62°  F.     The 
size  of  the  balls  is  such  that  the  temperature  of  the  water  is 
raised  from  62°  to  64°  F.  by  the  heat  contained  within  the 
ball.     It  will  be  found  that  the  mercury  will  be  raised  from 
62°  to  122°  F.     That  is,  the  same  amount  of  heat  that  raises 
10  pounds  of  water  2°  raises  10  pounds  of  mercury  60°,  or 
through  a  range  of  temperature  thirty  times  as  great.     It  is 
plain,  therefore,  that  to  raise  a  pound  of  mercury  from  62° 
to  63°  F.  requires  one-thirtieth  the  heat  necessary  to  raise  a 
pound  of  water  from  62°  to  63°  F.     Hence,  we  say  the  spe- 
cific heat  of  the  mercury  is  one-thirtieth,  or  .0333. 

EXAMPLE  1.— It  is  found  that  to  raise  the  temperature  of  20  pounds 
of  iron  from  62°  to  63°  requires  2.276  B.  T.  U.;  what;  is  the  specific  heat 
of  iron? 

SOLUTION.— To  raise  20  Ib.  of  water  from  62°  to  63°  requires  20 
B.  T.  U.  The  specific  heat  of  the  iron  is,  according  to  the  definition,  the 
ratio  between  the  quantities  of  heat  required  to  warm  the  iron  and  the 
water,  respectively,  through  1°;  that  is,  it  is  the  ratio  2.276  :  20  =  2.276 
-=-  20  =  .1138.  Ans. 

EXAMPLE  2.— The  specific  heat  of  silver  is  .057;  how  many  B.  T.  U. 
are  required  to  raise  22  pounds  of  silver  from  50°  to  60°? 

SOLUTION. — To  raise  the  temperature  of  a  pound  of  water  1° 
requires  1  B.  T.  U.  Since  the  specific  heat  of  silver  is  .057,  only 
.057  B.  T.  U.  is  required  to  raise  1  Ib.  of  silver  1°.  Hence,  to  raise 
22  Ib.  of  silver  10°  must  require  .057  X  22  X  10  =  12.54  B.  T.  U.  Ans. 

40.  Rule. — To  find  the  number  of  B.   T.   17.  required  to 
raise  the  temperature  of  a  body  a  given  number  of  degrees,  nnilti- 
ply  the  specific  heat  of  the  body  by  its  weight,  in  pounds,  and  by 
the  number  of  degrees. 


§5 


PROPERTIES  OF  GASES 


21 


Let        U  =  number  of  B.  T.  U.  required; 

c  =  specific  heat; 

W  =  weight; 

t    =  temperature  before  heat  is  applied; 

/,  =  temperature  after  heat  is  applied. 
Then,  U  =  c  W  (/t  -  /) 

The  specific  heats  of  some  of  the  more  common  substances 
are  given  in  Table  III,  which  follows. 

TABLE    III 


Substance 

Specific 
Heat 

Substance 

Specific 
Heat 

Water  

I.OOOO 

Tin     

.0562 

Sulphur  

.2026 

Mercury     

.0333 

Iron  

.1138 

Lead  

.0314 

Copper 

.0951 

Ice      

.5040 

Silver  

.0570 

41.  The  specific  heats  of  the  more  common  mine  gases 
are  given  in  Table  IV  (see  page  22). 

These  specific  heats  are  all  referred  to  water  as  unity. 
Taking  as  unity  the  quantity  of  heat  necessary  to  raise  the 
temperature  of  1  pound  of  water  1°  F.  at  its  maximum 
density,  columns  1  and  2  of  Table  IV  show  the  quantity  of 
heat  (B.T.  U.)  that  will  produce  the  same  rise  of  tempera- 
ture in  an  equal  weight  of  each  of  the  several  mine  gases 
for  ordinary  temperatures.  Column  3  shows,  likewise,  the 
quantity  of  heat  (B.  T.  U.)  necessary  to  produce  the  same 
rise  of  temperature  in  a  volume  of  each  gas,  equal  to  the 
volume  of  a  pound  of  air  at  the  same  constant  pressure. 
The  specific  heats  given  in  column- 1  of  Table  IV,  for  equal 
weights  and  constant  pressure,  are  those  determined  by 
.ictual  experiment  by  the  most  reliable  authorities;  they  are 
mostly  based  on  the  experiments  of  Regnault.  The  specific 
heats  given  in  column  2  of  the  table,  for  equal  weights  and 
constant  volume,  have  been  derived  by  calculation  from  the 
specific  heats  in  column  1  for  constant  pressure,  by  dividing 


22 


PROPERTIES  OF  GASES 


§5 


§5  PROPERTIES  OF  GASES  23 

the  latter  by  1.405,  which  is  the  most  generally  accepted  ratio 
for  the  specific  heat  of  a  gas,  for  constant  pressure,  to  the 
specific  heat  for  constant  vohime. 

The  figures  given  in  column  3  express  the  relative  heats  for 
equal  volumes  of  gas  and  air  at  constant  pressure,  instead  of 
equal  weights.  These  are  not,  therefore,  strictly  speaking, 
specific  heats,  but  are  generally  so  termed.  The  values  in 
this  column  have  been  derived  by  calculation  by  multiply- 
ing the  specific  heats  in  the  first  column  by  the  specific 
gravity  of  the  gas. 

42.  The  specific  heat  of  a  gas  varies  as  the  gas  is  allowed 
to  expand  (constant  pressure)  or  is  confined  in  a  given  space, 
or  volume  (constant  volume).     When  the  gas  is  allowed  to 
expand,  its  specific  heat  is  always  higher  than  when  it  is 
confined,   owing  to    the    decrease  of   pressure  and  density 
caused  by  the  expansion  of  the  gas.     These  two  conditions 
are  referred   to  as  specific  heat   under  constant  pressure   and 
specific  heat  under  constant  volume. 

The  specific  heat  of  gases  is  not  constant,  but  varies  with  the 
temperature  of  the  gas,  increasing  as  the  temperature  rises. 
It  is  stated  by  some  reliable  authorities  that  at  a  temperature 
of  1,200°  F.  the  specific  heat  of  carbon  dioxide  is  practically 
double  that  given  in  Table  IV.  This  gas  is  probably  more 
sensitive  in  this  respect  than  any  of  the  other  gases.  The 
specific  heat  of  steam  or  aqueous  vapor  increases  very  rapidly 
above  212°  F.  The  specific  heats  of  the  simple  gases  and  of 
air  do  not  increase  as  rapidly  at  the  higher  temperatures. 

43.  Latent  heat  is  the  heat  absorbed  without  change 
of  temperature  when  a  substance  changes  its  form  from  a 
solid    to    a   liquid,    or   from    a    liquid    to  a  gaseous    form. 
Examples  of  latent  heat  are  the  latent  heat  of  fusion,  when  a 
solid  becomes  a  liquid,   as  when  ice  melts   to  water,   and 
latent  heat  of  vaporization,  when  a  liquid  body  becomes  a 
gas,  as  in  the  generation  of  steam  from  water. 

44.  Careful  experiments  show  that  about  144  B.  T.  U.  are 
required  to  change  a  pound  of  ice  at  32°  F.  to  water  at  32°  F.; 
hence,  the  latent  heat  of  water  is  144  B.  T.  U. 


24  PROPERTIES  OF  GASES  §5 

Experiment  has  also  shown  that  965.8  B.  T.  U.  are  required 
to  convert  a  pound  of  water  at  212°  F.  into  steam  at  212°  F.; 
hence,  the  latent  heat  of  steam  is  965.8  B.  T.  U.  The  quan- 
tity of  heat  absorbed  by  a  substance  when  changing  from  a 
solid  to  a  liquid,  or  from  a  liquid  to  a  gaseous  form,  is  again 
given  out  when  the  gas  is  condensed  to  a  liquid  or  the  liquid 
becomes  a  solid. 

45.  Total  Heat. — The  total  quantity  of  heat  absorbed 
by  any  substance,  solid,  liquid,  or  gas,  in  changing  its  tem- 
perature or  passing  from  one  state  to  another,  may  be  cal- 
culated by  the  following  rule: 

Rule. — Multiply  the  specific  heat  of  each  form  of  the  sub- 
stance by  the  respective  number  of  degrees  of  change,  of  tempera- 
ture, and  add  to  the  product  the  total  number  of  B.  T.  U. 
expressing  the  latent  heat  absorbed  in  each  change  of  form  that 
takes  place.  Multiply  this  sum  by  the  weight  of  the  substance. 
The  last  product  will  be  the  total  quantity  of  heat  absorbed  by 
the  substance. 

EXAMPLB  1. — How  much  heat  will  be  required  to  melt  a  cubic  foot 
of  ice,  or  to  convert  a  cubic  foot  of  ice  at  32°  F.  into  water  at  32°  F.? 

SOLUTION.— The  specific  gravity  of  ice  is  .92  (Table  I);  the  weight 
of  a  cubic  foot  of  ice  is,  then,  62.5  X  .92  =  57.5  Ib.  The  latent  heat  of 
ice  being  144  B.  T.  U.,  the  total  heat  required  to  melt  this  weight 
of  ice  is  57.5  X  144  =  8,280  B.  T.  U. 

EXAMPLE  2. — Supposing  no  heat  to  be  lost  during  the  operation, 
(a)  how  many  gallons  of  boiling  water  at  sea  level  will  be  required  to 
melt  a  cubic  foot  of  ice  at  32°  F.,  so  that  the  resulting  temperature  of 
the  water  will  be  32°  F.?  (b}  how  many  gallons  of  water  will 
result  finally? 

SOLUTION. — (a)  The  fall  in  the  temperature  of  the  water  is 
212°  -  32°  =  180°  F.;  1  Ib.  of  water  will  therefore  yield  180°  B.  T.  U., 
and  to  produce  8,280  B.  T.  U.  will  require  sf/^  =  46  Ib.  Since  231 
cu.  in.  =  1  gal.,  and  1,728  cu.  in.  =  1  cu.  ft.,  1  cu.  ft.  contains  ¥/r 
=  7.48  gal.;  and  since  1  cu.  ft.  of  water  weighs  62.5  Ib.,  1  gal.  weighs 

^|  =  8.355  Ib.;  hence,  46  Ib.  of  water  will  equal  ^|^  =  5.5+  gal.  Ans. 
7.4o  o.oou 

(6)     The   weight   of    the  ice  being  57.5  Ib.,   the   total   weight   of 

water    produced    will    be    46  +  57.5     =     103.5    Ib.,    or    ^|  X  7.48 

K*«O 
=  12.38+  gal.    Ans. 


§5  PROPERTIES  OF  GASES 


EXAMPLES    FOR    PRACTICE 

1.  How  much  heat  is  absorbed  in  converting  100  pounds  of  water 
at  a  temperature  of  60°  F.  into  steam  at  212°  F.? 

Ans.  111,780  B.  T.  U. 

2.  Find  the  quantity  of  heat  given  out  by  a  bar  of  iron  weighing 
150  pounds,  in  cooling  from  300°  F.  to  60°  F.       Ans.  4,096.8  B.  T.  U. 

3.  How  many  B.  T.  U.  will  be  given  up  by  50  pounds  of  steam  at 
212°  F.  in  condensing  to  water  and  cooling  to  a  temperature  of  75°  F.? 

Ans.  55,140  B.  T.  U. 


EXPANSION  OF  BODIES  BY  HEAT 

46.  The  volume  of  any  body — solid,  liquid,  or  gaseous — 
is  always  changed  if  the  temperature  is  changed;  nearly  all 
bodies  expand  when  heated,  and  contract  when  cooled.     In 
solids  having  definite  figures,  the  expansion  may  be  consid- 
ered  in   three    ways,   according    to    the    conditions:     linear, 
expansion,  where  the  expansion  is  in  one  direction,  as  the  elon- 
gation   of    an    iron  bar;    surface  expansion,  where   the    area 
is  increased;  and  cubical  expansion,  where  the  increase  in  the 
whole  volume  is  considered. 

47.  Coefficients    of    Expansion. — The    coefficient 
of  linear  expansion  for  a  body  is  the  amount  of  linear 
expansion  that  a  unit  length  of  the  body  undergoes  when 
its  temperature  is  raised  1°.     The  coefficient  of  surface 
expansion  is  the  increase  in  area  that  a  unit  area  under- 
goes on   raising  its  temperature    1°.     The  coefficient  of 
cubical  expansion  is  the  increase  in  volume  that  a  unit 
volume  of  a  body  undergoes  on  raising  its  temperature  1°. 

48.  Table  V  gives  the  coefficients   of  expansion  for  a 
number  of  solids,   mercury,  and   alcohol,  and  the   average 
cubical  expansion  of   gases.     No  liquids  are  given,  except 
mercury  and  alcohol,  for  the  reason  that  the  coefficient  of 
expansion  for  liquids  is  different  at  different  temperatures. 


26 


PROPERTIES  OF  GASES 


§5 


TABLE  V 
TABLE    OF    COEFFICIENTS    OF    EXPANSION 


Name  of  Substance 

Linear 
Expansion 

c, 

Surface 
Expansion 

c, 

Cubical 
Expansion 

c. 

Cast  iron   .... 

.00000617 

.00001234 

.00001850 

Copper  

.00000955 

.00001910 

.00002864 

Brass  
Silver  

.00001037 
.00000690 

.00002074 
.00001390 

.00003112 
.00002070 

Bar  iron  
Steel  (untempered)  . 
Steel  (tempered)  .  . 
Zinc  

.00000686 
.00000599 
.00000702 
.00001634 

.00001372 
.00001198 
.00001404 
.00003268 

.00002058 
.00001798 
.00002106 
.00004903 

Tin 

000014  10 

00002820 

00004229 

Mercury  

.00003334 

.00006668 

.OOOIOOIO 

Alcohol  
Gases  ....'... 

.00019259 

.00038518 

.00057778 

.00203252 

49.     The  following  formulas  may  be  used  to  calculate  the 
amount  of  expansion: 

l=LCtt          (1) 
a  =  AC.t  (2) 

v  =   VC3t          (3) 
in  which  L  =  length  of  any  body; 

/   =  amount  of   expansion  or  contraction  due  to 

heating  or  cooling  the  body; 
A  =  area  of  any  section  of  the  body; 
a  =  increase  or  decrease  of  area  of  same  section 

after  heating  or  cooling  the  body; 
V  =  volume  of  body; 
v    =  increase  or  decrease  in  volume  due  to  heating 

or  cooling  the  body; 

C,  C,  C,  =  coefficients  of  expansion  taken  from  Table  V; 
/  =  difference  of  temperature,  in  degrees   F.,  of 
body  before  and  after  it  has  been  heated 
or  cooled. 


§5  PROPERTIES  OF  GASES  27 

EXAMPLE. — How  much  will  a  bar  of  untempered  steel  14  feet  long 
expand,  if  its  temperature  is  raised  80°? 

SOLUTION.— Since  only  one  dimension  is  given,  that  of  length,  linear 
expansion  only  can  be  considered.  From  Table  V,  the  coefficient  of 
linear  expansion  per  unit  of  length  for  a  rise  in  temperature  of  1°  is 
found  to  be  .00000599  for  untempered  steel.  Hence,  using  formula  1, 
I  =  LCit,  and  substituting,  14  X  .00000599  X  80  =  .0067088  ft.,  or 
.0067088  X  12  =  .0805056  in.  Ans. 

,50.  Volume  of  Gases. — The  volume  of  a  given  weight 
of  gas  depends  on  its  temperature  and  the  pressure  to  which 
it  is  subjected.  The  relation  between  the  temperature,  vol- 
ume, and  pressure  of  a  gas  is  an  important  one,  and  is 
expressed  by  two  laws,  known  as  Gay-Lussac's,  or  Charles's, 
law,  Art.  52,  and  Mariotte's,  or  Boyle's,  law,  Art.  63.  The 
pressure  that  a  gas  exerts,  or  its  expansive  force,  is  usually 
expressed  in  pounds  per  square  inch. 

51.  The  effect  of  heat  on  all  gases  is  to  increase  their 
volume.     Experiment   has   shown   that,  when  the  pressure 
remains  constant,  the  volume  of  a  gas  expands  or  contracts 
Te~o  of  its  volume  at  0°  F.  for  each  degree  of  change  in  tem- 
perature, and  this  rate  of  expansion  or  contraction  has  been 
found  uniform  through  all  practicable  ranges  of  temperature. 
Since  the  rate  of  change  is  true  whatever  the  volume  of  the 
gas,  if  we  have  a  volume  of  460  cubic  feet  at  0°  F.,  the  expan- 
sion or  contraction  for  this  volume  will  be  1  cubic  foot  for 
each  degree  rise  or  fall  in  temperature.     If  the  temperature 
is  lowerered  460°  to  the  absolute  zero,  it  is  evident  that,  as 
the  temperature  cannot  be  below  the  absolute  zero,  that  point 
will  also  be  the  lowest  limit  at  which  contraction  can  take 
place.     This  has  given  rise  to  another  definition  for  the  abso- 
lute zero  of  the  temperature  scale,  viz.,  the  point  from  which 
the  expansion  of  air  and  gases  proceeds  or  is  calculated. 

52.  Volume  and  Temperature  of  Gases. — The  law 

expressing  the  relation  existing  between  the  temperature 
and  volume  of  any  given  weight  of  gas  at  a  constant  pres- 
sure is  known  as  Gay-Lmssac's,  or  Charles's,  law.  This 
law  may  be  stated  as  follows: 


28  PROPERTIES  OF  GASES  §5 

Gay-Lussac's  Iiaw.  —  The  pressure  remaining  the  same, 
the  volume  of  any  given  quantity  of  gas  is  proportional  to  its 
absolute  temperature. 

Expressed  as  a  proportion,  this  law  is, 
*.:*»•  (460  +  /,)  :  (460  +  O  ,  or  -°- 


in  which      v,  =  volume  of  gas  at  temperature  /,; 

z/!  =  volume  of  the  same  gas  at  temperature  /,. 

EXAMPLE.—  If  10,000  cubic  feet  of  air  at  32°  F.  is  heated,  while 
passing  through  a  mine,  to  a  temperature  of  60°  F.,  what  is  the 
increased  or  expanded  volume  of  this  air? 

SOLUTION.  —  If  v,  is  the  required  expanded  volume,  at  the  tem- 
perature 60°,  then  substituting  the  given  values  in  the  formula, 

v,  =  10,000  -!      :  or,  v,  =  10,000  X         =  10,569  cu.  ft.    Ans. 


ATMOSPHERIC    PRESSURE 

53.  The  atmosphere  surrounding  the  earth,  like  all  other 
matter,  is  acted  on  by  gravity,  causing  what  is  called  atmos- 
pheric pressure. 

The  pressure  on  each  square  inch  of  surface,  due  to  the 
weight  of  the  atmosphere,  is  14.7  pounds  at  sea  level,  and 
decreases  at  higher  elevations.  Air  being  a  fluid,  transmits 
this  pressure  equally  in  all  directions;  in  other  words,  atmos- 
pheric pressure  is  not  only  exerted  downwards  as  weight, 
but  with  equal  force  sidewise  and  upwards. 

54.  The  upward  pressure  of  the  atmosphere  is  well  illus- 
trated in  Fig.  7.     Here  a  glass  tumbler  is  filled  with  water 
to  the  brim,  and  a  piece  of  stiff  paper  placed  over  it,  in  con- 
tact with  the  surface  of  the  water,  so  as  to  exclude  all  air. 
The  paper  is  held  in  position  while  the  tumbler  is  inverted; 
the  upward  pressure  of  the  atmosphere  on  each  square  inch 
of  the  surface  of  the  paper,  as  indicated  by  the  arrows,  sup- 
ports the  weight  of  the  water  in  the  tumbler. 


§5 


PROPERTIES  OF  GASES 


55.     Measurement  of  Atmospheric  Pressure. — The 

principle  utilized  for  measuring  the  pressure  of  the  atmos- 
phere is  illustrated  in  Fig.  8.  A  glass  tube  about  3  feet  long 
and  closed  at  one  end  is  filled  with  mercury.  The  tube  is 
inverted  and  the  open  end  placed  in  a  cup  of  mercury  with 
the  end  dipping  beneath  the  surface.  The  mercury  in  the 
tube  will  fall  and  come  to  rest  with  the  top  of  the  column  at 


FIG.  7 


a  height  of  about  30  inches  above  the  surface  of  the  mercury 
in  the  cup.  This  column  of  mercury  is  supported  by  the 
pressure  of  the  atmosphere  on  the  surface  of  the  mercury  in 
the  cup.  The  upper  end  of  the  tube  contains  no  air,  so  that 
there  is  no  opposing  force  except  the  weight  of  the  column 
of  mercury.  The  two  forces  are  in  delicate  equilibrium  and 


30 


PROPERTIES  OF  GASES 


§5 


any  variation  in  the  atmospheric  pressure  causes  a  corre- 
sponding variation  in  the  length  of  the  mercury  column  to 
maintain  the  equilibrium. 

If  water  had  been  used  instead  of  mercury, 
since  mercury  has  a  specific  gravity  of  13.6,  the 
height  of  the  column  of  water  to  balance  the 
pressure  of  the  atmosphere  would  have  been 
30  X  13.6  =  408  inches  =  34  feet.  That  is,  if  a 
tube  were  filled  with  water,  inverted,  and  placed 
in  a  dish  of  water  in  a  manner  similar  to  the 
experiment  made  with  the  mercury,  the  resulting 
height  of  the  column  of  water  would  be  34  feet. 

56.  The  Mercurial  Barometer. — The  mer- 
curial barometer  is  an  instrument  for  measuring 
atmospheric  pressure,  and  the  principle  on  which 
it  works  is  that  described  in  the  preceding  article. 
Fig.  9  is  a  common  form  in  which  the  glass  tube 
is  placed  within  a  metal    casing    having   a  slot 
opening  provided    with    a  sliding  vernier    at  the 
top  of  the  tube,  and  a  glass  cylinder  for  observing 
the    level  of    the   mercury    in    the    basin    at   the 
bottom  of  the  tube.     This  basin  generally  consists 
of  a  metallic  rim  to  which  is  secured  a  chamois- 
skin  bag  for  holding  the  mercury. 

57.  Adjustment. — The  level  of  the  mercury 
in  the  cup  or  basin  at  the  bottom  of  the  tube  is 
adjusted  by  means  of  the  screw  at  the  lower  end 
of  the  instrument.     By  means  of  this  screw  pres- 
sing on  the  bottom  of  the  chamois-skin  bag,  the 
level    of    the   mercury    in    the    cup    is   raised   or 
lowered.     It  is  thus  adjusted  until  a  fixed  metallic 
point,  or  needle,  projecting  downwards  from  the 
metallic    casing    within     the     glass    cylinder    is 

FlG-9  observed  to  indent  the  surface  of  the  mercury. 
This  point  forms  the  zero  of  the  scale,  and  when  the  surface 
of  the  mercury  in  the  cup  has  been  adjusted,  the  height  of 
the  mercury  column  is  read  from  the  scale  by  adjusting  the 


§5  PROPERTIES  OF  GASES  31 

movable  vernier  to  the  upper  surface  of  the  column.  The 
movement  of  the  vernier  is  controlled  by  the  thumbscrew 
shown  near  the  top  of  the  instrument.  A  thermometer  is 
adjusted  to  the  metal  casing  of  the  barometer  to  indicate  the 
temperature  of  the  observation.  After  reading  the  barom- 
eter, the  atmospheric  pressure,  in  pounds  per  square  inch,  is 
calculated  by  multiplying  the  barometric  height  by  the  weight 
of  1  cubic  inch  of  mercury,  which  may  be  assumed  at  ordi- 
nafy  temperatures  as  approximately  .49  pound  (.4911  pound 
at  32°  F.).  Thus,  the  atmospheric  pressure  corresponding 
to  30  inches  of  mercury  is  .49  X  30  =  14.7  pounds  per 
square  inch. 

58.  It  is  common,  in  estimating  the  pressure  supported 
by  any  gas  or  air,  to  speak  of  such  pressure  as  so  many 
atmospheres,  and  it  is  quite  common  practice  to  consider 
that  one   atmosphere  equals  a  pressure  of  15  pounds  per 
square  inch;  a  pressure  of  30  pounds  per  square  inch  is  then 
two  atmospheres,  45  pounds  three  atmospheres,  etc.     This 
pressure  is  the  absohite  pressure  or  the  total  pressure  sup- 
ported by  the   gas  or  air  in   question,  and  not  the  gauge 
pressure. 

59.  The  Vacuum. — The  space  in  the  tube  above  the 
mercury  column,  Fig.  8,  is  called  a  vacuum,  meaning  an 
empty  space.      This   space  is  practically  a  perfect  vacuum, 
being  entirely  empty  of  air  or  other  substance.     It  is  custom- 
ary to  measure  or  describe  a  vacuum  by  the  inches  of  mercury 
supported  by  atmospheric  pressure  against  it.     To  make  this 
clear,  suppose  that  a  small  quantity  of  air  or  gas  is  allowed 
to  enter  the  space  above  the  mercury  column.      However 
small  the  quantity  may  be,  it  will  at  once  fill  the  entire  space, 
and  the  mercury  column  will  be  lowered  more  or  less,  accord- 
ing to  the  quantity  of  air  entering  the  tube.     The  tension  of 
this  expanded  air  causes  a  slight  pressure  on  the  top  of  the 
mercury  column,  thus  balancing  a  portion  of  the  atmospheric 
pressure  and  lowering  the  column  of  mercury  supported  by 
it.      The   space  is   then   called  a  partial  vacuum,  and  is 
measured  or  described  by  the  height  of  the  mercury  column 


32  PROPERTIES  OF  GASES  §5 

supported  by  atmospheric  pressure  against  it;  this  is  the 
principle  of  the  vacuum  gauge.  Since  the  atmospheric 
pressure  decreases  as  we  ascend  above  sea  level,  a  perfect 
vacuum  will  be  indicated  by  a  shorter  mercury  column;  thus, 
at  an  elevation  of  10,000  feet  above  sea  level  the  atmospheric 
pressure  supports,  under  normal  conditions,  20.92  inches  of 
mercury.  At  this  elevation,  20.92  inches  of  mercury  will 
indicate  a  perfect  vacuum.  Changes  in  atmospheric  con- 
ditions also  alter  the  height  of  the  mercury  column  indicating 
a  perfect  vacuum.  For  example,  at  sea  level,  the  height 
of  the  mercury  column  will  vary  from  29  to  31  inches,  accord- 
ing to  atmospheric  conditions. 

60.  Vacuum  Gauge. — The  vacuum  gauge  is  used  to 
measure  the  vacuum  produced  in  the  working  of  pumps,  con- 
densers, etc.      With  the  most  perfect  machinery,  it  is  not 
possible  to  obtain  a  perfect  vacuum,  there  being,  as  a  rule,  a 
small  amount  of  air  remaining  that  gives  a  back  pressure  on 
the  pump  or  engine  of  3,  4,  5,  etc.  pounds  per  square  inch, 
according  to  the  character  of  the  work  and  the  machine. 

61.  The   Aneroid   Barometer. — The    aneroid  barom- 
eter, Fig.  10,  consists  of  a  cylindrical  metal  box,  or  vacuum 
chamber,  hermetically  sealed.     The  face  of  this  box  is  of 
thin,  elastic,  corrugated  metal;  when  the  atmospheric  pres- 
sure increases,  this  plate  is  pressed  inwards,  and  when  it  is 
diminished  it  is  forced  outwards  by  its  own  elasticity,  aided 
by  a  spring  beneath.     These  movements  of  the  plate  are 
transmitted  and  multiplied  by  a  combination  of  levers  that 
act  on  an  index  hand  and  cause  it  to  move  over  a  graduated 
dial.     These  barometers  are  self-correcting  (compensated) 
for  variations  in  temperature,  and  are  very  portable,  occupy- 
ing but  a  small  space.     The  mercurial  barometer  is,  however, 
the  standard.     Most  aneroid  barometers  have  two  concen- 
tric scales,  as  shown  in  Fig.  10:  the  outer,  or  altitude,  scale 
starting  from  0  and  giving  the  elevation  above  sea  level  to 
the  nearest  10  feet;  and  the  inner,  or  mercury,  scale  giving 
the  atmospheric  pressure  in  inches,  tenths,  and  hundredths, 
usually  from  27  inches  to  33  inches,  corresponding  to  the 


PROPERTIES  OF  GASES 


33 


readings  of  the  mercurial  barometer.  The  outer,  or  altitude, 
scale  is  often  made  so  that  it  can  be  moved  by  the  milled 
screw  shown,  and  its  zero  set  to  correspond  to  any  desired 
reading  on  the  mercury  scale.  Some  barometers  have  a 
small  thermometer  attached  to  the  dial,  and  from  its  reading, 
a  correction  for  temperature  can  be  made.  This  correction, 
however,  is  usually  omitted  in  preliminary  work.  Formulas 


FIG.  10 

and  tables  for  determining  it  are  to  be  found  in  most  engi- 
neers' pocketbooks. 

62.  Gauge  Pressure. — In  considering  the  expansive 
force  of  air,  steam,  and  other  gases,  it  is  customary  to  meas- 
ure the  pressure  they  exert  above  the  atmospheric  pressure 
by  some  form  of  gauge  especially  designed  for  the  purpose. 
Water  gauges  are  used  for  light  pressures;  compressed-air 
gauges,  manometers,  and  different  forms  of  spring  gauges 

145—4 


34  PROPERTIES  OF  GASES  §5 

are  used  for  the  higher  pressures.  The  pressure  indicated 
by  such  a  gauge  is  called  the  gauge  pressure,  and  it  is 
evident  that  the  total  pressure  supported  by  gas— that  is, 
the  absolute  pressure — is  the  atmospheric  pressure  plus  the 
gauge  pressure. 

63.     Volume     and     Pressure    of     Gases. — The    law 

expressing  the  relation  existing  between  the  pressure  and 
volume  of  any  given  quantity  of  gas  at  a  constant  tempera- 
ture is  known  as  Marlotte's?  or  Boyle's,  law. 

Mariotte's  Law. — The  temperature  remaining  the  same, 
the  volume  of  any  given  quantity  of  gas  is  inversely  proportional 
to  its  absolute  pressure. 

Expressed  as  a  proportion,  this  law  is  z>,  :  v,  =  pt:  /„  or 
?!  =  A. 

Vi          p» 

hence,  v.  =  Vl(&]          (1) 

(2) 

in  which  v,  =  volume  corresponding  to  an  absolute  pres- 
sure p,;  , 

Vi  =  volume  corresponding  to  an  absolute  pres- 
sure PL 

EXAMPLE. — When  the  atmospheric  pressure  is  14.7  pounds  per 
square  inch,  what  volume  of  free  air  must  be  compressed  into  a  cyl- 
inder having  a  capacity  of  20  cubic  feet  to  give  a  gauge  pressure  of 
80  pounds  per  square  inch  in  the  cylinder,  assuming  the  temperature 
to  remain  constant? 

SOLUTION. — Calling  z/2  the  required  quantity  of  free  air  at  atmos- 
pheric pressure,  and  substituting  the  given  values  in  formula  1, 
80  +  14.7 


20  X 


14.7 


v,  =  20  X  ~  =  128.84  cu.  ft.     Ans. 

64.     "Volume,  Temperature,  and  Pressure  of  Gases. 

In  the  preceding  articles,  it  has  been  found  that  the  ratio  of 
the  volumes  is  equal  to  the  ratio  of  the  absolute  temperatures, 
or  the  inverse  ratio  of  the  absolute  pressures,  the  pressure 


§5  PROPERTIES  OF  GASES  35 

or  the  temperature  in  each  respective  case  remaining  con- 
stant. It  may  happen  that  both  pressure  and  temperature 
may  change,  in  which  case  the  ratio  of  the  volumes  will  be 
equal  to  the  product  of  the  ratio  of  the  absolute  tempera- 
tures and  the  inverse  ratio  of  the  absolute  pressures,  or 

(1) 
A 


in  which  v,  =  volume  corresponding  to  the  absolute  pres- 
sure A  and  the  absolute  temperature  T, 
(or  460  +  /,); 

Vt  =  volume  corresponding  to  the  absolute  pres- 
sure A  and  the  absolute  temperature  7\ 
(or  460  +  /J. 

EXAMPLE.  —  At  an  elevation  of  10,000  feet  above  sea  level,  the  atmos- 
pheric pressure  is  practically  10  pounds  per  square  inch.  At  this  ele- 
vation, how  many  cubic  feet  of  free  air  at  a  temperature  of  32°  F.  must 
be  compressed  into  a  cylinder  having  a  capacity  of  20  cubic  feet,  to 
give  a  gauge  pressure  of  80  pounds  per  square  inch  —  assuming  that 
the  temperature  of  the  compressed  air  has  risen  to  60°  P.? 

SOLUTION.—  Calling  v,  the  required  quantity  of  free  air  at  atmos- 
pheric pressure,  and  substituting  the  given  values  in  formula  2, 

460  +  32      10  +  80 
X  460  +  60  X  "~iO  ~~ 

v,  =  20  X  ^  X  ^  =  170.3  cu.  ft.    Ans. 

O/U        1U 

65.  Temperature  and  Pressure  of  Gases.  —  So  far, 
air  has  been  considered  free  to  expand  or  contract.  It  is 
also  necessary  to  consider  the  effect  of  a  change  of  tem- 
perature and  pressure  of  air  in  a  confined  space  where  the 
volume  is  constant.  In  this  case,  the  ratio  of  the  absolute 
temperatures  is  equal  to  the  ratio  of  the  absolute  pressures, 
or 

7\  =  A 
T>       A 

EXAMPLE.—  The  temperature  of  compressed  air  falls  in  the  trans- 
mission of  the  air  from  the  compressor  to  the  drills  from  80°  F.  at  the 
compressor  where  the  gauge  pressure  is  60  pounds,  to  50°  F.  at 


36  PROPERTIES  OF  GASES  §5 

the  drills;  find  the  gauge  pressure  available  for  operating  the  drills. 
The  plant  is  located  at  an  elevation  of  5,000  feet  above  sea  level, 
where  the  atmospheric  pressure  is,  say,  12.2  pounds  per  square  inch. 
SOLUTION.— Calling  /,  the  required  pressure  at  the  drills,  and  sub- 
stituting the  given  values  in  the  formula, 

»•' -»•*-«•««>•  A- 


MIXTURE    OF    GASES 

66.  Mixtures  of  Gases  of  the  Same  Temperature 
and  Pressure. — When  two  or  more  gases  are  mixed,  there 
will  be  no  change  of  pressure  unless  there  is  a  change  in  the 
temperature  or  total  volume  of  the  gases;  or,  in  other  words, 
when  two  or  more  gases  having  the  same  temperature  and 
pressure  are  mixed  without  changing  the  total  volume,  the 
pressure  of  the  mixture  will  be  the  same  as  that  of  the  gases 
before  mixing. 

For  example,  if  1  cubic  foot  of  air,  at  a  temperature  of 
32°  F.  and  pressure  of  5  pounds  per  square  inch,  and  1  cubic 
foot  of  methane  (marsh  gas),  also  at  a  temperature  of  32°  F. 
and  at  5  pounds  per  square  inch  pressure,  are  made  to  occupy 
a  vessel  of  just  2  cubic  feet  capacity  without  any  change  in 
the  temperature,  the  pressure  of  the  mixture  will  also  be 
5  pounds  per  square  inch. 

67.  Mixtures  of  Equal  Volumes  of  Gases  Having 
Unequal  Pressures. — If  two  gases  having  the  same  vol- 
ume and  temperature,  but  different  pressures,  be  mixed  in  a 
vessel  whose  volume  equals  one  of  the  equal  volumes  of  the 
gas,  the  pressure  of  the  mixture  will  be  equal  to  the  sum  of 
the  two  pressures,   provided  that  the  temperature  remains 
the  same  as  before. 

EXAMPLE.— Two  vessels  containing  3  cubic  fee'  oi  gas,  each  at  a 
temperature  of  60°,  and  at  a  pressure  of  40  pounds  and  25  pounds  per 
square  inch,  respectively,  are  placed  in  communication  with  each 
other,  and  all  the  gas  is  compressed  into  one  vessel.  If  the  tempera- 
ture of  the  mixture  is  also  60°,  what  is  the  pressure? 

SOLUTION.— According  to  the  law  just  given,  the  pressure  will  be 
40  +  25  =  65  Ib.  per  sq.  in. 


§5  PROPERTIES  OF  GASES  37 

68.     Mixtures  of  Two  Gases  Having  Unequal  Vol- 
umes and  Pressures. — In  this  case,  the  relations  of  the 
pressures  and  volumes  can  best  be  shown  by  an  equation. 
Let  v  and  p    =  volume  and  pressure  of  one  gas; 

Vi  and/>!  =  volume  and  pressure  of  the  other  gas; 
V  and  P  =  volume  and  pressure  of  the  mixture. 
Then,  if  the  temperature  remains  the  same, 

P  V  =  p  v  +  pi  v, 
p=  pv+p.v.  (1) 

V 

V-^^          (2> 

EXAMPLE  1. — Two  gases  of  the  same  temperature,  having  volumes 
of  7  cubic  feet  and  4^  cubic  feet,  and  tensions  of  25  pounds  and  18 
pounds  per  square  inch,  respectively,  are  mixed  together  in  a  vessel 
whose  volume  is  10  cubic  feet;  the  temperature  remaining  the  same, 
what  is  the  resulting  pressure? 

256 


per  sq.  in.     Ans. 

EXAMPLE  2.  —  What  must  be  the  volume  of  a  vessel  that  will  hold 
two  gases  whose  volumes  are  7  cubic  feet  and  4£  cubic  feet,  and  whose 
pressures  are  25  pounds  and  18  pounds  per  square  inch,  respectively, 
in  order  that  the  pressure  may  be  25.6  pounds  per  square  inch,  the 
temperature  remaining  the  same  throughout? 


SOLUTION.-     V  -  -  =  W  cu  .f  t.    Ans. 


38  PROPERTIES  OF  GASES  §5 


CHEMISTRY  OF  GASES 


GENERAL  PRINCIPLES 

69.  Chemistry  is  that  branch  of  science  which  treats  of 
the   composition   of    substances   and    the    alterations    they 
undergo    in   their   composition,   by  a  change  in   the  kind, 
number,  and  relative  position  of  their  atoms. 

From  a  chemical  standpoint  at  least,  the  atom  is  not 
divisible,  and  is,  therefore,  always  simple  or  composed  of 
the  same  kind  of  matter.  The  molecule,  being  formed  by 
the  union  of  two  or  more  atoms,  may  be  either  simple  or  com- 
pound, according  as  the  atoms  forming  the  molecules  of  a 
substance  are  like  or  unlike.  When  they  are  like,  the  sub- 
stance is  an  element  or  elementary;  when  unlike,  it  is  a 
compound. 

70.  Atomic    Weight. — The   atoms    of   every   element 
have  a  definite  weight,  but  this  weight  differs  for  different 
elements.     Atoms  are  so  small  that  they  cannot  be  weighed 
directly,  but  their  weights,  relative  to  the  weight  of  the  atom 
of  some  element  chosen  as  a  unit,  can  be  determined.     The 
atom  of  hydrogen  is  commonly  chosen  as  the  standard  because 
hydrogen  is  the  lightest  known  element.     When,  for  example, 
an  atom  of  an  element  is  found  to  be  sixteen  times  as  heavy 
as  an  atom  of  hydrogen,  it  is  said  to  have  an  atomic  weight 
of  16;    or  if    twenty-three  times  as   heavy  as  an  atom  of 
hydrogen,  its  atomic  weight  is  said  to  be  23,  and  so  on.     It 
must  be  remembered  that  atomic  weight  is  simply  relative 
weight  and  not  the  actual  weight  of  the  atoms. 

71.  Symbols. — For  the   sake  of  convenience,  the   dif- 
ferent elements  are  expressed  by  letters,  called  symbols. 
These  symbols  are  usually  the  first  letter  of  the  name  of  the 
element;  for  example,  H  stands  for  hydrogen,  O  for  oxygen. 
C  for  carbon.     When  several  elements  begin  with  the  same 


§5 


PROPERTIES  OF  GASES 
TABLE  VI 


39 


Element 

Sym- 
bol 

Atomic 
Weight 
H  =  i 

Element 

S£T 

Atomic 
Weight 
//=  i 

Aluminum    .    . 

Al 

26.9 

Neodymium     . 

Nd 

142.5 

Antimony     .    . 

Sb 

II9-3 

Neon     .... 

Ne 

19.9 

Argon    f    .    .    . 

A 

39-6 

Nickel   s    .    .    . 

Ni 

58.3 

Arsenic     .    .    . 

As 

74-4 

Nitrogen  .    .    . 

N 

13.93 

Barium      .    .    . 

'Ba 

136.4 

Osmium    .    .    . 

Os 

189.6 

Bismuth    .    .    . 

Bi 

206.9 

Oxygen     .    .    . 

O 

15.88 

Boron    »    .    .    . 

B 

10.9 

Palladium     .    . 

Pd 

105-7 

Bromine    . 

Br 

79.36 

Phosphorus 

P 

30.77 

Cadmium      .    . 

Cd 

in.  6 

Platinum  .    .    . 

Pt 

193.3 

Caesium     .    .    . 

Cs 

I3I-9 

Potassium     .    . 

K 

38.85 

Calcium     .    .    . 

Ca 

39-7 

Praseodymium 

Pr 

139.4 

Carbon      .    .    , 

C 

11.91 

Radium     .    .    . 

Rd 

223.3 

Cerium      .    .    . 

Ce 

139.2 

Rhodium  .    .    . 

Rh 

IO2.2 

Chlorine    .    .    . 

Cl 

35-iS 

Rubidium     .    . 

Rb 

84.9 

Chromium    .    . 

Cr 

51-7 

Ruthenium  .    . 

Ru 

IOO.9 

Cobalt   .... 

Co 

58.55 

Samarium     .    . 

Sm 

149.2 

Columbium  .    . 

Cb 

93.3 

Scandium      .    . 

Sc 

43-8 

Copper      .    .    . 

Cu 

63.1 

Selenium  .    .    . 

Se 

78.6 

Erbium      .    .    . 

Er 

164.8 

Silicon  .... 

Si 

28.2 

Fluorine    .    .    . 

F 

18.9 

Silver    .... 

Ag 

107.11 

Gadolinium  .    . 

Gd 

154-8 

Sodium     .    .    . 

Na 

22.88 

Gallium     .    .    . 

Ga 

69.5 

Strontium     .    . 

Sr 

86.94 

Germanium 

Ge 

72. 

Sulphur     .    .    . 

S 

31.82 

Glucinum      .    . 

Gl 

9-03 

Tantalum      .    . 

Ta 

181.6 

Gold  

Au 

195.7 

Tellurium     .    . 

Te 

126.6 

Helium      .    .    . 

He 

4- 

Terbium    .    .    . 

Tb 

158.8 

Hydrogen     .    . 

H 

I.OOO 

Thallium  .    .    . 

Tl 

202.  6 

Indium      .    .    . 

In 

114.1 

Thorium   .    .    . 

Th 

230.8 

Iodine    .... 

I 

1  2.6.  01 

Thulium    .    .    . 

Tm 

169.7 

Iridium      .    .    . 

Ir 

191.5 

Tin     

Sn 

118.1 

Iron 

Fe 

ce   e 

Titanium 

Ti 

47.7 

Krypton    .    .    . 

Kr 

3  D  O 
81.2 

Tungsten      .    . 

W 

H  /  •/ 
182.6 

Lanthanum  .    . 

La 

137-9 

Uranium   .    .    . 

U 

236.7 

Lead      .... 

Pb 

205.35 

Vanadium     .    . 

V 

50.8 

Lithium     .    .    . 

Li 

6.98 

Xenon'  .... 

Xe 

127. 

Magnesium  .    . 

Mg 

24.18 

Ytterbium     .    . 

Yb 

I7I.7 

Manganese  .    . 

Mn 

54-6 

Yttrium     .    .    . 

Yt 

88.3 

Mercury    . 

HZ 

198.5 

Zinc    

Zn 

64.9 

Molybdenum    . 

Mo 

95-3 

Zirconium     .    . 

Zr 

89.9 

40 


PROPERTIES  OF  GASES 


§5 


letter,  as,  for  example,  carbon,  calcium,  chlorine,  copper,  etc., 
one  only  of  these  elements  is  expressed  by  the  first  letter, 
the  others  being  expressed  by  two  letters;  thus,  C  for  carbon, 
Ca  for  calcium,  Cl  for  chlorine,  Cu  for  copper;  Some- 
times the  symbol  is  an  abbreviation  of  the  Latin  name  of  the 
element;  for  example,  copper  (Latin,  cuprum),  Cu;  iron 
(Latin,  ferrum),  Fe;  silver  (Latin,  argentum],  Ag. 

When  a  single  letter  forms  a  symbol,  such  letter  must  be 
written  as  a  capital;  when  two  letters  are  used  as  a  symbol 
the  first  letter  is  always  a  capital  and  the  second  letter  is 
always  a  small  letter.  The  symbol  of  an  element  standing 
alone  always  expresses  a  single  atom;  thus,  //"expresses  one 
atom  of  hydrogen,  O  one  atom  of  oxygen,  etc.  When  it  is 
necessary  to  express  more  than  one  atom,  it  is  done  by  pla- 
cing a  small  figure,  called  a  subscript,  to  the  right  of  and  a 

TABLE  VII 


Element 

Sym- 
bol 

Atomic 
Weight 

Element 

Sym- 
bol 

Atomic 
Weight 

Calcium     .    .    . 

Ca 

40 

Nitrogen     .    . 

N 

M 

Carbon  .... 

C 

12 

Oxygen   .    .    . 

O 

16 

Chlorine    .    .    . 

Cl 

35 

Phosphorus    . 

P 

31 

Copper  .... 

Cu 

63 

Silicon     .    .    . 

Si 

28 

Hydrogen     .    . 

H 

I 

Sodium    .    .    . 

Na 

23 

Iron    

Fe 

56 

Sulphur  .    .    . 

S 

32 

Lead 

Pb 

206 

Tin 

Sn 

118 

Mercury    .    .    . 

Hg 

199 

Zinc     .... 

Zn 

65 

little  below  the  symbol;  Ht  means  two  atoms  of  hydrogen, 
H3  three  atoms  of  hydrogen,  etc.  Sometimes  a  figure,  called 
a  coefficient,  is  placed  before  the  symbol  to  indicate  the 
number  of  atoms,  as  2(9,  BO,  etc. 

72.  Table  VI   gives    the  names,   symbols,   and   atomic 
weights  of  all  the  elements  now  known. 

73.  For    such  .calculations   as    are    necessary   in    most 
mining  work,  the  approximate  atomic  weights  of  the  most 


§5  PROPERTIES  OF  GASES  41 

common  elements  given  in  Table  VII  are  sufficiently  accu- 
rate, and  should  be  used  in  solving  examples  relating  to 
mine  gases. 

74.  Chemical  Compounds. — A  chemical  compound  is 
a    substance  composed  of   unlike  atoms  united   in   definite 
fixed  proportions,  according  to  chemical  laws,  that  give  to 
the  atoms  of  each  element  certain  combining  powers.     For 
example,  water  is  a  chemical  compound,  being  always  formed 
by  the  union  of  two  atoms  of  hydrogen  and  one  atom  of 
oxygen. 

In  like  manner,  when  one  atom  of  carbon  unites  with  one 
atom  of  oxygen,  carbon  monoxide  (often  called  carbonic 
oxide)  CO  is  formed;  but  when  one  atom  of  carbon  unites 
with  two  atoms  of  oxygen,  carbon  dioxide  (often  called  car- 
bonic acid)  CGt  is  produced.  These  gases  are  both  chemical 
compounds,  each  having  different  properties. 

NOTE. — The  compound  CO  was  formerly  known  as  carbonic  oxide, 
but  this  name  does  not  describe  the  compound  and  does  not  agree  with 
the  naming  of  compounds  as  now  used  by  chemists.  The  term  car- 
bonic oxide  has  therefore  been  given  up  universally  in  chemical  litera- 
ture and  is  being  rapidly  done  away  with  in  all  scientific  and  technical 
literature:  the  term  carbon  monoxide  has  been  substituted  for  it. 
This  name  means  that  one  atom  of  carbon  is  combined  with  one  atom 
of  oxygen. 

The  compound  CO,  was  formerly  called  carbonic  acid,  but  this 
name  has  also  been  given  up,  for  a  similar  reason,  in  scientific  and 
technical  literature  and  the  term  carbon  dioxide  substituted.  This 
term  means  that  one  atom  of  carbon  is  combined  with  two  atoms  of 
oxygen.  The  modern  terms  will  be  used  in  this  Section,  although  the 
old  terms  will  usually  be  given  in  parentheses  to  avoid  confusion,  as 
the  older  terms  are  used  in  much  of  the  older  mining  literature  and 
many  of  the  mine  examining  boards  still  adhere  to  them. 

Again,  when  one  atom  of  carbon  unites  with  four  atoms 
of  hydrogen,  methane,  commonly  known  as  carbureted 
hydrogen,  or  marsh  gas  C//«,  results;  but,  when  two  atoms  of 
carbon  unite  with  the  four  atoms  of  hydrogen,  ethylene,  or 
ethene,  commonly  known  as  olefiant  gas  C,//«,  is  produced. 
These  are  all  examples  of  chemical  compounds,  as  are  also 
salt,  blue  vitriol,  nitric  acid,  etc.,  for  they  are  all  formed  by 
the  chemical  union  of  unlike  atoms. 

75.  Mechanical    Mixtures. — A    mechanical    mixture 
is   not   a    chemical   compound,   being   composed  of   unlike 


42  PROPERTIES  OF  GASES  §5 

molecules  simply  mixed  together  instead  of  unlike  atoms 
chemically  united.  The  molecules  of  the  different  substances 
forming  the  mixture  are  mixed  in  any  proportions,  and  the 
mixture  has  properties  varying  with  the  proportion  of  the 
ingredients.  The  atmosphere  about  us  is  a  good  example 
of  a  mechanical  mixture,  as  we  shall  see  later,  for  it  consists 
principally  of  oxygen  and  nitrogen  gases,  mixed  in  a  free 
state  and  having  no  chemical  bond  of  union. 

76.  Mixtures  of  some  liquids,  if  allowed  to  stand,  will 
remain  mixed,  but  others,  on  standing,  will  separate  and  the 
several  liquids  arrange  themselves  in  accordance  with  their 
specific  gravities.     Mixtures  of  gases,  however,  are  perma- 
nent,  and  when  once  two    or  more    gases  are    thoroughly 
mixed  there  is  no  separation  of  the  gases  in  the  mixture. 
This  property  of  the  mixing  of  gases  is  an  important  one, 
for,  if  a  mixture  of  gases  acted  like  mixtures  of  most  liquids, 
and  the   several  ingredients  of    the  mixture  separated  on 
standing,   life    on    the    earth   would  be  impossible,   as    the 
heavy  carbon  dioxide  or  carbonic-acid    gas  in    the    atmos- 
phere would  separate  from  the  other  gases  composing  the 
atmosphere  and  form  a  layer  next  to  the  surface  in  which 
the  present  forms  of  animal  life  could  not  exist. 

77.  Expressing  a  Molecule  by  Symbols. — The  mole- 
cules of  all  elements  that  exist  ordinarily  as  gases  consist 
each  of  two  like  atoms;  for  example,  the  molecule  of  hydrogen 
consists  of  two  atoms  (.//,).    This  is  not  true  of  all  molecules 
of  the  solid  elements;  as  the  molecules  of  mercury,  cadmium, 
and  zinc  contain  only  one  atom,  while  those  of  phosphorus 
and  arsenic  contain  four  atoms,  etc.     The  molecules  of  a 
compound  may  contain  two  or  more  atoms,  according  to  the 
nature  of  the  atoms  in  combination. 

A  compound  molecule  is  expressed  by  writing  the  symbols 
of  the  elements  composing  it  together  and  indicating  by 
means  of  subscripts  the  number  of  atoms  of  each  element 
present.  Such  an  expression  is  called  a  chemical  for- 
mula. A  molecule  of  water  is  composed  of  two  atoms  of 
hydrogen  and  one  atom  of  oxygen,  and  its  formula  is  H,O\  a 


PROPERTIES  OF  GASES 


43 


molecule  of  sulphuric  acid  consists  of  two  atoms  of  hydro- 
gen, one  atom  of  sulphur,  and  four  atoms  of  oxygen,  and 
its  formula  is  H*SOt.  When  more  than  one  molecule  is 
to  be  indicated,  a  coefficient  is  placed  before  the  formula,  as 
1H,O  means  two  molecules  of  water.  Table  VIII  gives  the 
formulas  and  number  of  atoms  in  the  molecules  of  various 
compounds. 

TABL.E  VIII 


Name  of  Compound 

For- 
mula 

Number 
of  Atoms 
in  One 
Molecule 

Carbon-monoxide  gas  (carbonic-oxide)  .  . 
Carbon-dioxide  gas  (carbonic-acid)  .... 
Ammonia  gas 

CO 
CO, 
NHa 

2 

3 

4" 

Carbureted  hydrogen  (methane,  or  marsh  gas) 
Ethylene  or  olefiant  gas  
Sulphuric  acid 

CH. 
CM. 
HtSO. 

5 
6 
7 

The  molecules  of  some  organic  or  carbon  compounds  con- 
tain a  far  greater  number  of  atoms  than  is  expressed  in 
Table  VIII.  The  correct  symbol  for  those  substances  com- 
mon to  mining  must  be  memorized  as  met  with. 

78.  Moleculai*  Weight. — Since  a  molecule  of  any  com- 
pound contains  a  definite  number  of  atoms,  it  is  plain  that  all 
molecules  of  the  same  substance  have  the  same  weight.  The 
molecular  weight  of  a  compound  is  the  weight  of  the  molecule, 
as  compared  with  the  weight  of  an  atom  of  hydrogen,  and  is 
equal  to  the  sum  of  the  atomic  weights  of  the  elements  com- 
posing the  molecule,  each  taken  as  many  times  as  there  are 
atoms  of  that  element  in  the  molecule.  For  example,  the 
molecular  weight  of  sulphuric  acid  H^SO*  is  found  as  follows: 

SULPHURIC  ACID 

ff,  =     2  X    1  =      2 

S   =  32  X    1  =  32 

04  =    4  X  16  =  (U 

Molecular  weight  =  98 


44 


PROPERTIES  OF  GASES 


§5 


Table  IX  gives  the  molecular  weights  of  some  of  the  most 

common  gases. 

TABLE    IX 


Substance 

Molecule 

Molecular  Weight 

Hydrogen  

ft. 

(2  X  i) 

=      2 

Oxygen   

o, 

(2  X  16) 

=   32 

Nitrogen 

Nt 

(2  X  14) 

=    28 

Marsh  gas  (carbureted  hydrogen  or 
methane)        

CH< 

12  +  (4  X  i) 

=  16 

Olefiant  gas  

CtHt 

(2  X  12)  +  (4X1) 

=  28 

Carbon  monoxide  (carbonic  oxide)  . 
Carbon  dioxide  (carbonic  acid)     .    . 
Hydrogen  sulphide     

CO 
CO, 
H,S 

12  +  16 

12+  (2  X  16) 
(2X1)+  32 

=  28 
=  44 
=  34 

Ammonia  gas  

NHa 

14+  (3  X  i) 

=  17 

79.  Percentage  Composition. — It  is  often  necessary 
to  calculate  the  percentage  composition  of  a  substance  from 
its  chemical  formula.  For  example,  it  may  be  desired  to 
know  the  percentage,  by  weight,  of  hydrogen  in  a  given 
weight  of  marsh  gas,  or  it  may  be  desired  to  calculate  the 
weight  or  carbon  dioxide  formed  in  burning  a  given  weight 
of  coal,  and  to  determine  therefrom  the  volume  of  the  gas 
produced.  The  percentage,  by  weight,  of  any  element  of  a 
substance  is  equal  to  the  atomic  weight  of  such  element 
multiplied  by  the  number  of  atoms  of  the  element  in  the 
molecule,  divided  by  the  molecular  weight  of  the  substance, 
and  the  result  multiplied  by  100.  Expressed  as  a  formula, 
this  rule  is, 

w  X  100 


per  cent.  = 


W 


in  which  w  —  total  weight  of  any  element  in  substance  = 
atomic  weight  of  the  element  X  the  number 
of  atoms  of  that  element  in  the  molecule; 
W  =  molecular  weight  of  substance. 

EXAMPLE  1. — Find  the  percentage  of  hydrogen  in  marsh  gas 
(methane)  and  the  weight  of  hydrogen  contained  in  10  pounds  of 
this  gas. 

SOLUTION. — The  symbol  expressing  a  molecule  of  marsh  gas  is  C7/4; 
we  have,  then, 


§5  PROPERTIES  OF  GASES  45 

Parts  by  weight  of  hydrogen  //« 4X1=4 

Parts  by  weight  of  carbon  C =  12 

Molecular  weight  of  marsh  gas  Cfft =16 

The  percentage,  by  weight,  of  hydrogen  in  marsh  gas  is,  then, 

TS  X  100  =  25  per  cent.     Ans. 

The  weight  of  hydrogen  in  10  pounds  of  marsh  gas  is 
10  X  £?s  =  2.5  Ib.     Ans. 

EXAMPLE  2. — Find  the  weight  of  water  that  can  be  formed  from  2.5 
pounds  of  hydrogen. 

SOLUTION. — The  symbol  expressing  a  molecule  of  water  is  f/,O, 
and  we  have, 

Parts  by  weight  of  hydrogen  //, 2X1=    2 

Parts  by  weight  of  oxygen  O =16 

Molecular  weight  of  water  H,O =18 

Hence,  the  percentage  of  H  is  A  X  100  =  ¥£  =  11$  per  cent. 

Then  ll£  per  cent.  :  100  per  cent.  =  2.5  Ib.  :  x. 

Weight  =  2.5  X  jji  =  2.5  X  9  =  22.5  Ib.     Ans. 

NOTE.— It  should  be  observed  in  these  two  examples  that  the  weight  of  water 
that  will  be  formed  in  the  complete  explosion  of  10  pounds  of  marsh  gas  has  been 
calculated. 


EXAMPLES    FOR    PRACTICE 

1.  What  percentage  by  weight  of  carbureted  hydrogen  (marsh  gas) 
CHt,  is  pure  hydrogen?  Ans.  25  per  cent. 

2.  If   the   specific   gravity   of   carbureted   hydrogen   (marsh  gas) 
(Table  I)  is  .559,  what  weight  of  hydrogen  will  be  contained  in  1,000 
cubic  feet  of  this  gas,  at  a  temperature  of  60°  F.,  barometer  30  inches? 

Ans.  10.701  Ib.,  nearly. 

3.  If  all  fhe  hydrogen  in  example  2  were  to  unite  with  oxygen  (in 
the  proportion  of  two  atoms  of  hydrogen  to  one  atom  of  oxygen)  to 
form  water,  what  weight  of  water  would  be  produced? 

Ans.  96.309  Ib. 

4.  What  weight  of  carbon  is  contained  in  100  cubic  feet  of  carbon 
monoxide  CO,  a  [molecule  of  this  gas  containing  one  atom  of  carbon 
and  one  atom  of  oxygen,  temperature  =  60°  F.,  barometer  30  inches? 

Ans.  3.173  Ib. 


80.  Avogadro's  IJaw. — The  Italian  physicist,  Avoga- 
dro,  in  1811,  established  the  law  that  equal  volumes  of  all 
substances,  either  elementary  or  compound,  when  in  the  gaseous 


46  PROPERTIES  OF  GASES  §5 

state  and  at  the  same  temperature  and  pressure,  contain  an  equal 
number  of  molecules. 

From  this  law,  it  follows:  (1)  That  the  molecules  of  all 
gaseous  bodies  must  be  of  equal  size.  (2)  That  the  weight 
of  any  gaseous  molecule — compared  with  that  of  a  molecule  of 
hydrogen — is  proportional  to  the  weight  of  any  given  volume 
compared  with  an  equal  volume  of  hydrogen;  and  conversely, 
that  the  weights  of  equal  volumes  of  any  gases  are  propor- 
tional to  the  molecular  weights  of  the  gases. 

If,  for  instance,  1  cubic  foot  of  marsh  gas  weighs  8  times 
as  much  as  1  cubic  foot  of  hydrogen,  one  molecule  of  marsh 
gas  must  weigh  8  times  as  much  as  one  molecule  of  hydrogen; 
and  conversely,  if  the  above  law  is  true,  since  the  molec- 
ular weight  of  marsh  gas  is  16  and  that  of  hydrogen  is  2, 
1  cubic  foot  of  marsh  gas  weighs  -^  =  8  times  as  much  as 
1  cubic  foot  of  hydrogen.  Hence,  we  have  the  following 
general  rule: 

Rule. — The  density  of  any  gas,  simple  or  compound,  when 
referred  to  hydrogen  as  unity,  is  equal  to  one-half  its  molecular 
•weight. 

81.  Density  of  Mine  Gases. — In  Table  X  are  given 
the  molecular  weights  and  densities,  referred  to  hydrogen, 
of  the  important  mine  gases,  including  the  gases  that  form 
the  atmosphere,  and  hydrogen  gas,  which  is  the  standard 
for  density. 

82.  Chemical  Reactions. — All  substances  are  liable  to 
chemical  change,   particularly  when  molecules  of  different 
kinds  are  brought  into  intimate  contact  under  proper  con- 
ditions.   Any  change  in  the  arrangement  of  the  atoms  among 
molecules  is  termed  a  chemical  reaction.     The  ease  with 
which  chemical  reactions  take  place  differs  with  different  sub- 
stances.    Compounds  that  react  with  difficulty  are  said  to  be 
stable;  those  that  react  with  ease  are  said  to  be  unstable. 

83.  Chemical  Equations. — A  chemical  equation  is  an 
equation  expressing  the  reaction  that  takes  place  between 
two  or  more  substances.     Since  every  chemical  change  or 


§5 


PROPERTIES  OF  GASES 


47 


reaction  is  simply  an  alteration  in  the  number  or  position  of 
the  atoms  within  the  molecules,  and  consequently  a  change 
in  the  constitution  of  the  molecules,  a  reaction  may  be 
expressed  by  an  equation  of  the  formulas  entering  into  and 

TABLE  X 


Gas      . 

Molecular 
Weight 

Density  Referred  to 
Hydrogen 

Hydrogen  Ht  .            .... 
Oxygen  O  
Nitrogen  N,    
Carbureted  hydrogen 
Methane                          CHt 

2 
32 
28 

16 

I 
16 
14 

g 

Marsh  gas  
Olefiant  gasl  -  .... 

28 

Ethylene    .  J 
Carbon  monoxidel  ~~ 
Carbonic  oxide  .  J 
Carbon  dioxide!  ~_ 
Carbonic  acid    J 
Hydrogen  sulphide  .    .  1       _ 
Sulphureted  hydrogen  J 

28 
44 
34 

M 

22 

17 

resulting  from  the  reaction.  The  substances  entering  into 
the  reaction  are  called  the  factors;  those  resulting  from  the 
reaction  are  called  the  products.  The  equation  representing 
a  reaction  is  written  according  to  the  following  rule: 

Rule. — Place  the  formulas  of  the  factors,  connected  by  the 
sign  of  plus,  as  the  first  member  of  the  equation,  and  the  for- 
mulas of  the  products,  also  connected  by  the  sign  of  plus,  as  the 
second;  and  finally  indicate  by  means  of  coefficients  the  num- 
ber of  molecules  of  the  factors  and  of  the  products. 

84.  Writing  Chemical  Equations. — One  of  the  most 
important  reactions  in  mining  is  that  which  takes  place  in  the 
complete  explosion  of  firedamp,  a  mixture  of  methane  (marsh 
gas)  and  air.  In  this  reaction,  the  gases  present  before  the 


48  PROPERTIES  OF  GASES  §5 

reaction  takes  place  are  methane  (marsh  gas)  CHt  and  air, 
the  air  consisting  chiefly  of  oxygen  O  and  nitrogen  N.  The 
gases  resulting  from  the  reaction  are  carbon  dioxide  (car- 
bonic-acid gas)  CO,,  moisture  H,O,  and  nitrogen  N.  In 
order  to  write  the  equation  representing  the  reaction  that 
takes  place,  the  gases  present  before  the  reaction  are  written 
for  the  first  member  of  the  equation,  and  those  resulting 
from  the  reaction  for  the  second  member;  and  the  equation 
reads:  CH.  +  O,  +  N,  =  CO,  +  H,O  +  N,.  It  will  be 
observed  that  in  this  equation  only  one  molecule  of  each  gas 
is  indicated,  since  the  number  of  molecules  of  each  gas 
required  to  satisfy  the  reaction  is  not  yet  known;  the  equation 
is,  therefore,  not  complete. 

85.  The  carbon  and  the  hydrogen  of  the  methane  (marsh 
gas)  separate  from  each  other,  each  combining  with  the 
oxygen  of  the  air  to  form  carbon  dioxide  CO,  and  water 
H,O,  respectively.  The  nitrogen  of  the  air  is  neutral  and 
remains  unchanged.  It  will  be  noticed  that  sufficient  oxygen 
O  is  required  in  the  first  member  to  satisfy  all  the  carbon 
and  all  the  hydrogen  of  the  marsh  gas.  In  one  molecule  of 
marsh  gas  Cfft,  there  is  one  atom  of  carbon  C  and  four 
atoms  of  hydrogen  //«;  the  one  atom  of  carbon  C  takes  up 
two  atoms  of  oxygen  O,,  forming  one  molecule  of  carbon 
dioxide  CO,.  But  one  molecule  of  water  H,O  contains  two 
atoms  of  hydrogen  H,  and  one  atom  of  oxygen  O;  the  four 
atoms  of  hydrogen  Ht  will,  therefore,  form  two  molecules  of 
water  2U,O,  requiring  for  this  purpose  two  atoms  of  oxygen. 
The  total  oxygen,  therefore,  required  to  satisfy  both  the  car- 
bon and  the  hydrogen  of  the  marsh  gas  is  four  atoms,  or 
two  molecules  2(9.,.  But  since  the  nitrogen  and  oxygen  are 
present  in  air  in  the  ratio  of  4:1,  these  two  molecules  of 
oxygen  will  correspond  to  eight  molecules  of  nitrogen,  which 
latter  gas  is  present,  but  takes  no  part  in  the  reaction.  To 
complete  the  equation,  therefore,  write  before  each  term  the 
figure  indicating  the  number  of  molecules;  thus,  CHt  +  1O, 
+  SN,  =  CO,  +  2H*O  +  8N,.  That  the  equation  is  now 
complete  is  shown  by  the  fact  that  there  is  the  same  number 


§5  PROPERTIES  OF  GASES  49 

of  each  kind  of  atoms  on  each  side  of  the  equation;  that  is, 
the  equation  is  balanced. 

86.  Change  of  Volume  of  Gases  Due  to  Chemical 
Changes. — Chemical  reactions  of  gases  are   often   accom- 
panied by  a  change  in  the  volume  of  the  gases.     The  vol- 
ume of  the  gases  before  the  reaction  takes  place  may  be 
greater  or  less   than  that  of  the  gases  resulting  from  the 
reaction.     For  example,  when  1  cubic  foot  of  nitrogen  gas 
and  3  cubic  feet  of  hydrogen  gas  are  intimately  mixed  and 
caused  to  combine  chemically  by  an  electric  spark,  there  is 
formed  2  cubic  feet  only  of  ammonia  gas  NH3.     Here  the 
original  volume  of  4  cubic  feet  has  been  reduced  to  2  cubic 
feet.     When  2  cubic  feet  of  hydrogen  and  1  cubic  foot  of 
oxygen  are  intimately  mixed  and  caused  to  combine  chemi- 
cally by  an  electric  spark,  there  results  2  cubic  feet  of  water 
vapor.    The  original  3  cubic  feet  of  gases  are  here  reduced  to 
2  cubic  feet.     It  must  be  remembered  that  taking  the  volume 
of  the  hydrogen  atom  as  unity,  the  volume  of  any  gaseous 
atom  is  one  and  the  volume  of  any  gaseous  molecule  is  two, 
regardless  of  the  number  of  atoms  that  have  united  to  form 
the  molecule,  as  is  shown  by  the  examples  given  above. 

87.  Calculation  of  Change  of  Volume. — The  change 
of  volume  of  a  gas  due  to  any  chemical  reaction  can  be  cal- 
culated by  the  aid  of  Avogadro's  law,  Art.  80,  as  follows: 
First  write  the  equation  expressing  the  reaction.     The  num- 
ber of  molecules  of  the  factors  in  the  equation  represent 
the  volume  before  the  reaction;  the  number  of  molecules 
of  the  products  represent  the  volume  after  the  reaction. 

For  illustration,  take  the  reaction  for  the  formation  of 
ammonia  NH>  already  given. 

N.  +  3J7,  =  27V7/, 
1+3  2 

Here  there  were  present  1  volume  or  molecule  of  nitrogen 
and  3  volumes  or  molecules  of  hydrogen,  which,  when  com- 
bined, resulted  in  2  volumes  or  molecules  of  ammonia. 

88.  In  calculating  the  change  of  volume  of  the  explosion 
of  carbon  monoxide  (carbonic  oxide)  in  air,  we  have, 

145—5 


50  PROPERTIES  OF  GASES  §5 

ICO  +  O,  +  4AT,  =  2CO,  +  4N, 

214  24 

Before  the  explosion  there  are,  for  the  factors,  2+1  +  4 
=  7  volumes  of  gas;  after  the  explosion  there  are,  for  the 
products,  2  +  4  =  6  volumes  of  gas. 

This  principle  should  be  used  for  calculating  the  changes 
of  volume  for  all  reactions  between  gases. 

EXAMPLE.— (a)  How  many  cubic  feet  of  carbon  dioxide  (carbonic 
acid)  will  be  formed  from  the  explosion  of  500  cubic  feet  of  marsh  gas 
C//*  in  air  at  constant  temperatures  and  pressures?     (b)   How  many 
cubic  feet  of  oxygen  will  be  consumed  in  forming  the  CO,? 
SOLUTION.— (a)  The  reaction  representing  the  explosion  is 
CHt  +  2O,  +  BN,  =  CO,  +  2H,O  +  8N, 

128128 

From  this  it  is  seen  that  1  volume  of  C7/«  produces  1  volume  of  CO,; 
hence,  500  volumes  of  CHt  produce  500  volumes  of  CO,.  Ans. 

(b)     Since,  as  seen  from  the  reaction,  1  volume  of  CHt  requires 

2  volumes  of  oxygen  for  its  complete  combustion,  and  one-half  of  this 

is  for  the  combustion  of  the  carbon,  1  volume  is  required  for  1  volume 

of  CHt\  hence,  for  500  cu.  ft.  of  CH*,  500  cu.  ft.  of  oxygen  is  required. 

Ans. 

EXAMPLES    FOR    PRACTICE 

In  the  following  examples,  assume  constant  temperature  and 
pressure. 

1.  How  many  cubic  feet  of  oxygen  will  be  consumed  in  the  forma- 
tion of  100  cubic  feet  of  carbon  monoxide  (carbonic-oxide)  gas  CO? 

Ans.  50  cu.  ft. 

2.  If  the  hydrogen  in  100  cubic  feet  of  ammonia  gas  were  set  free, 
what  volume  would  it  make?  Ans.  150  cu.  ft. 

3.  The  formula  for  ethylene,  or  olefiant  gas,  is  C,fft;  what  volume 
of  oxygen  will  be  required  to  convert  100  cubic  feet  of  this  gas  into 
CO,  and  ff,O?  Ans.  300  cu.  ft. 

89.     Change  of  Pressure  Due  to  Change  of  Volume. 

The  change  in  volume  due  to  any  chemical  reaction  is  always 
accompanied  by  a  change  of  pressure  and  temperature.  To 
calculate  this  change  of  pressure,  calculate  first  the  change 
of  volume  as  explained  in  the  preceding  article,  then  assume 
that  the  temperature  is  constant,  and  calculate  the  pressure 
at  the  new  volume  by  the  formulas  in  Art.  63. 


§5 


PROPERTIES  OF  GASES 


EXAMPLE. — Calculate  the  change  of  pressure  due  to  the  chemical 
change  of  volume  in  an  explosion  of  carbon-monoxide  gas  CO,  accord- 
ing to  the  equation  given  in  Art.  88. 

SOLUTION.— In  Art.  88,  it  was  found  that  in  this  explosion  the 
volume  was  reduced  in  the  ratio  of  7  :  6;  hence,  if  pt  =  pressure  after 
the  explosion  and  /,  the  pressure  before  the  explosion,  from  for- 
mula 2,  Art.  63,  pt  =  p1  -,'  we  have, 


THE  ATMOSPHERE 

90.  Composition  of  the  Atmosphere. — An  analysis 
of  the  atmosphere  about  us  shows  it  to  consist  of  a  mixture 
of  oxygen  and  nitrogen,  with  varying  amounts  of  carbon 
dioxide  (carbonic-acid  gas)  and  ammonia.  The  oxygen  and 
nitrogen  are  always  free,  or  uncombined,  and  are  present  in 
the  proportions  given  in  Table  XI. 

TABLE    XI 


Gases  Forming  Air 

Parts  by  Volume 

Parts  by  Weight 

Nitrogen 

7Q  1 

77  O 

Oxygen         .... 

20.7 

23.0 

Total     

IOO.O 

IOO.O 

While  the  percentages  of  oxygen  and  nitrogen  remain 
practically  the  same,  there  is  a  varying  amount  of  carbon 
dioxide,  ammonia,  and  moisture  in  the  air  of  different  local- 
ities. For  example,  the  air  of  a  crowded  room  may  contain 
a  comparatively  high  percentage  of  carbon  dioxide;  mine  air 
may  likewise  be  laden  with  carbon  dioxide,  moisture,  and 
mine  gases  from  the  workings  of  the  mine. 

91.  Weight  of  1  Cubic  Foot  of  Air. — The  common 
formula  employed  in  mining  for  calculating  the  weight  of 
1  cubic  foot  of  air  is  based  on  the  weight  of  1  cubic  foot  of 
air  at  1°  F.  above  the  absolute  zero  and  an  atmospheric  pres- 
sure corresponding  to  1  inch  of  mercury.  This  weight  is 


52  PROPERTIES  OF  GASES  §5 

1.3273  pounds.  The  weight  of  1  cubic  foot  of  air  at  any  other 
temperature  and  pressure  is  found  by  multiplying  1.3273  by 
the  atmospheric  pressure  (inches  of  mercury),  and  dividing 
by  the  absolute  temperature. 

This  rule  expressed  as  a  formula  is, 
1.3273  B 
460 +  / 

in  which    w  =  weight  of  1  cubic  foot  of  air  at  a  tempera- 
ture /  and  barometric  pressure  B\ 
B  =  barometric  pressure,  inches  of  mercury; 
/    =  temperature  of  air,  degrees  F. 

92.  Density  of  Air  Referred  to  Hydrogen. — In  com 

paring  the  weights  of  equal  volumes  of  air  and  gas,  we 
observe  that  the  smallest  volume  of  air  that  we  can  take 
for  comparison  consists  of  four  molecules  of  nitrogen  4^,, 
and  one  molecule  of  oxygen  O^  making  five  molecules  of 
these  mixed  gases  that  we  call  air.  The  relative  weight  of 
these  five  molecules,  compared  to  that  of  five  molecules 
of  hydrogen  5//,,  will  give,  approximately,  the  density  of 
air  referred  to  hydrogen.  This  density  is  only  approximate 
because  of  small  traces  of  other  gases  in  the  atmosphere, 
but  it  is  sufficiently  close  for  practical  purposes.  The  cal- 
culation is  as  follows: 

SUBSTANCE  QUANTITY  SYMBOL         RELATIVE  WEIGHT 

Nitrogen  4  molecules  4AT,          4(2  X  14)  =  112 

Oxygen  1  molecule  O,  (2  X  16)  =     32 

Air  5  molecules  Total,          144 

Hydrogen         5  molecules  5ff,          5(2  X  1)     =     10 

Density  of  air  referred  to  hydrogen  W-  =  14.4. 

93.  Density  and  Specific   Gravity  of  Gases. — The 

terms  relative  density  and  specific  gravity,  as  referred  to 
gases,  are  similar,  the  former  referring  to  hydrogen  or  some 
other  unit  and  the  latter  to  air.  It  is  evident  that,  if  the  den- 
sity of  air,  referred  to  hydrogen,  is  14.4;  or,  in  other  words, 
if  air  is  14.4  times  as  heavy  as  hydrogen,  the  specific  gravity 

of  any  gas  referred  to  air  is  :rr7  of  its  density  referred  to 


§5 


PROPERTIES  OF  GASES 


53 


hydrogen.  By  this  means  it  is  possible  to  calculate  the 
specific  gravity  of  any  gas  from  its  molecular  weight  as 
shown  in  Table  XII. 

As  will  be  observed  by  comparing  the  calculated  specific 
gravities,  as  given  above,  with  the  true  specific  gravities  of 
these  gases  referred  to  air  as  determined  by  experiment, 
there  is  but  slight  difference  between  the  two,  and  this  is 
largely  due  to  the  approximate  figure  (14.4),  used  for  the 
derlsity  of  air  referred  to  hydrogen  and  to  the  fact  that  the 
densities  given  for  the  several  gases,  as  well  as  the  atomic 
weights  used,  are  only  approximate. 

TABTjE    XII 


Specific  Gravity 

Calculated 

Determined  by 
Experiment 

Hydrogen  H  

i 

—  =     .0694 

.0693 

Oxygen  O       

16 

16 
=  i.mo 
14.4 

I.I057 

Nitrogen  N 

14 

—  —   —        0722 

0714 

Methane,  (carbureted  hydro-  1     -_ 
gen  or  marsh  gas)   .   .    .  j 

8 

7Z^  =    '55s6 

•5590 

Ethylene  (olefiant  gas)  Cafft   .    . 

14 

^-   =      .9722 

.9700 

Carbon  monoxide  (carbonic-  1  _  _ 
oxide  gas)     \  C  U 

14 

-^~   =      -9722 

.9670 

Carbon  dioxide   (carbonic-  1  ,,  .» 
acid  gas)    }CO* 

22 

1^   =    *'W* 

1.5291 

Hydrogen     sulphide     (sul-1  ,.  „ 
phureted-hydrogen  gas)  j-"»^ 

I? 

&«* 

1.1912 

94.  Heat  of  Chemical  Reactions. — With  all  chemical 
reactions,  heat  is  either  given  out  or  absorbed,  thus  materially 
affecting  the  pressures  and  volumes  of  the  gaseous  products 
of  the  reaction.  The  amount  of  heat  given  out  or  absorbed 
in  like  reactions  is  always  the  same  between  equal  weights 
of  the  same  substances. 


54  PROPERTIES  OF  GASES  §5 

COMBUSTION 

95.  Combustion  is  the  act  of  burning.     As  commonly 
used,  it  means  the  combination  of  a  substance  with  oxygen, 
although  other  chemical  reactions  are  sometimes  included 
under  the  same  term.     Combustion  may  be  either  slow  or 
rapid.     Slow   combustion    is    attended    by    heat    only,    while 
rapid  combustion  is   generally   attended    by  heat  and   light. 
Examples  of  slow  combustion  are  found  in  the  consuming 
of  the  animal  tissues  of  the  body,  by  which  animal  heat  is 
produced;   and   in   the    slow  consumption   of   carbonaceous 
matter  and  fine  coal  in  the  gob  heaps  or  waste  of  a  mine, 
which  is  accompanied  by  heat  but  no  flame.      The  consu- 
ming of  any  substance  by  fire  furnishes  an  example  of  rapid 
combustion,  producing  heat  and  light. 

96.  Oxidation. — As  oxygen  is  the  great  supporter  of 
combustion,  the  process  of  combustion  is  often  called  oxida- 
tion.    While  there  is  a  similarity  between  combustion  and 
oxidation,  all  combustion  is  not  oxidation,  and  all  oxidation 
is  not  combustion.     For  example,   phosphorus  burning  in 
chlorine  gas  is  an  example  of  combustion  but  not  of  oxida- 
tion, while  the  corroding  of  iron  or  other  metal  surfaces  by 
the  action  of  the  atmosphere  is  an  example  of  oxidation,  but 
not   of   combustion    according   to    the  usual  acceptance    of 
the  term  combustion.     The  use  of  the  term  combustion  to 
describe  other  chemical  reactions  than  oxidation  is  unusual, 
and  will  not  be  used  in  this  Section,  so  that  by  combustion 
a  process  of  oxidation  will  always  be  meant.     Deoxidation, 
the  reverse  of  oxidation,  is  known  as  reduction. 

97.  Heat  of  Combustion. — A  given  weight  of  a  com- 
bustible gives  out  by  its  combustion  a  definite  amount  of 
heat.     The  heat  value  (calorific  value)  of  a  combustible  is 
expressed  by  the  number  of  heat  units  developed  in  burning 
a  pound  of  such  combustible.     Whether  the  combustion  is 
slow  or  rapid  the  same  quantity  of  heat  will  be  given  out  per 
unit  of  weight,  and  the  total  heat  generated  by  burning  any 
combustible  is  proportional  to  the* weight  of  combustible 


§5  PROPERTIES  OF  GASES  55 

burned.  Although  the  same  amount  of  heat  is  always  given 
out  by  the  combustion  of  a  given  weight  of  a  substance, 
the  temperature  produced  by  the  combustion  varies  greatly, 
depending  on  the  conditions  under  which  the  combustion 
takes  place;  in  slow  combustion,  much  of  the  heat  generated 
is  lost  by  radiation,  convection,  or  conduction;  the  more  rapid 
the  combustion  of  a  given  substance  the  higher  is  the  result- 
ing temperature. 

y8.  A  combustible  substance  is  one  that  will  burn; 
that  is,  all  the  elements  composing  it  will  combine  with  oxy- 
gen to  produce  heat.  The  products  of  combustion  are  usu- 
ally gaseous,  though  not  always  so.  Many  substances,  such 
as  coal,  although  mainly  composed  of  combustible  materials, 
contain  also  incombustible  portions  that  do  not  burn  and 
remain  as  ash  when  the  substance  is  burned. 

The  chief  combustible  elements  in  ordinary  fuels  are 
hydrogen  and  carbon,  and  the  chemical  reactions  express- 
ing the  combustion  are  given  in  the  following  paragraphs. 

99.  When  hydrogen  is  burned  in  air  or  oxygen,  water  is 
formed  according  to  the  reaction,  2H,  +  O,  =  ZH*O.     The 
heat  given  off  by  this  reaction  is  62,032  B.  T.  U.  per  pound 
of  hydrogen  burned. 

100.  When  carbon  burns,  any  one  of  three  reactions  may 
take   place:     (1)    In  an  ample    supply    of   oxygen,    carbon 
dioxide  (carbonic  acid)  CO*  is  formed  according  to  the  reac- 
tion C,  +  2O,  =  2CO,,  in  which  1  pound  of  carbon  burning 
to  carbon  dioxide  CO,  produces  14,600  B.  T.  U.     (2)   If  the 
supply  of  oxygen   is  deficient,  carbon  monoxide   (carbonic 
oxide)    CO   is    formed    according   to    the    reaction    C,  +  O, 
=  2  CO,  by  which  the  burning  of  1  pound  of  carbon  produces 
4,450  B.  T.  U.     (3)   When  there  is  too  little  oxygen  for  all 
the  carbon  to  burn  to  carbon  dioxide  CO,  and  more  than  is 
required  for  it  to  burn  to  CO,  a  mixture  of  CO,  and  CO  is 
formed. 

101.  In  burning  a  compound  of  carbon  and  hydrogen, 
as  marsh  gas  CHt,  in  a  plentiful  supply  of  air,  the  reaction 


56  PROPERTIES  OF  GASES  §5 

is  expressed  by  the  equation:  CH<  +  20,  +  SJV,  =  CO, 
+  2/f,0  +  8N,.  The  heat  given  out  in  this  case  is  23,513 
B.  T.  U.  per  pound  of  methane,  or  marsh  gas  CH^  burned. 
In  the  case  of  olefiant  gas  burned  in  oxygen,  the  reaction  is 
C#4  +  30,  =  ICO,  +  2tf,O.  The  heat  given  out  in  this 
case  is  21,344  B.  T.  U.  per  pound  of  ethylene,  or  olefiant  gas 
C,Hi,  burned. 

102.  Sulphur  burns  in  air  according  to    the   equation 
S  +  O,  =  SO,,    giving    out   4,050  B.  T.  U.    per   pound  of 
sulphur. 

103.  Table  XIII  gives  the  heating  value  (calorific  power) 
of  a  few  of  the  important  fuels  and  gases.     The  heating  value 
is  expressed  in  B.  T.  U.  per  pound  of  fuel. 

TABLE  XIII 


Substance 


Hydrogen  to  H,O 

Carbon  to  CO, 

Marsh  gas  to  H,O  and  CO, 
Carbon  monoxide  CO  to  CO, 

Anthracite 

Bituminous  coal 

Wood  (average  dry)     .    .    . 


B.  T.  U.  per  Pound 


62,032 
14,544 
23,513 

4,325 
12,600 
13,500 

8,000 


The  following  example  will  illustrate  the  use  of  this  table: 

EXAMPLE. — How  many  cords  of  wood  (hickory),  thoroughly  dry, 
and  having  a  calorific  power  of  6,000  B.  T.  U.  per  pound,  may  be 
considered  as  equivalent  to  1  ton  of  bituminous  coal  having  a  heating 
value  of  13,500  B.  T.  U.  per  pound? 

SOLUTION. — Assuming  the  weight  of  1  cord  of  hickory  as  4,500  lb., 
we  have,  for  the  relative  heating  value  of  a  ton  (2,000  lb.)  of  bitumi- 
nous coal  and  a  cord  of  hickory, 

2,000  X  13,500 
4,500  X  8,000"  =  l  C°rd 

Therefore,  1  cord  of  dry  hickory  may  be  considered  as  equivalent  to 
1  ton  of  bituminous  coal. 


§5  PROPERTIES  OF  GASES  57 

104.  Initial  Force  of  an  Explosion  of  Methane 
(Marsh  Gas). — The  chemical  equation  expressing  the 
reaction  that  takes  place  in  the  explosion  of  a  body  of  fire- 
damp at  its  most  explosive  point  is: 

BEFORE  EXPLOSION         AFTER  EXPLOSION 
CH<  +  2<9a  +  SN,  =  CO,  +  2tf,0  +  81V, 
Molecular  weight    .    .  16        64       224        44         36          224 

The  numbers  written  below  the  symbols  in  this  equation 
show  the  relative  weights  (molecular  weight),  respectively, 
of  the  different  gases  concerned  in  the  reaction.  For  each 
16  parts,  by  weight,  of  marsh  gas  exploded  there  are  formed 
the  following:  carbon  dioxide  CO,,  44  parts;  water  //a(9, 
36  parts;  nitrogen  N,  224  parts.  Hence,  for  each  pound 
of  methane  or  marsh  gas  that  is  burned  there  results 
H  =  2.75  pounds  of  carbon  dioxide  CO,;  ft  =  2.25  pounds 
of  water  H,O",  "W  =  14  pounds  of  nitrogen  N.  Knowing  the 
weight  of  each  of  the  gaseous  products  per  pound  of  marsh 
gas  burned,  it  is  possible  to  calculate  the  initial  temperature 
at  the  moment  of  explosion  as  follows:  Multiply  the  weight 
of  each  gas  formed  by  its  specific  heat;  the  sum  of  the  several 
products  thus  obtained  gives  the  number  of  B.  T.  U.  required 
to  raise  the  temperature  of  these  gases  1°  F.  Then,  divi- 
ding the  total  heat  (B.  T.  U.)  produced  by  the  burning  of 
1  pound  of  methane  (marsh  gas)  by  this  result,  gives  the 
rise  in  temperature  at  the  moment  of  explosion.  The  total 
heat  produced  by  the  burning  of  1  pound  of  marsh  gas  (see 
Art.  101)  has  been  found  to  be  23,513  B.  T.  U.  The  spe- 
cific heats  of  the  gases  as  given  in  Table  IV,  referred  to  water 
as  unity,  express  the  amount  of  heat  (B.  T.  U.)  required  to 
raise  1  pound  of  the  substance  1°  F.  Calculating  the  total 
heat  required  to  raise  the  temperature  of  the  gases  produced 
by  the  burning  of  1  pound  of  marsh  gas  1°  F.,  we  have, 

B.  T.  U. 

Carbon  dioxide  CO 2.75  X  .2170  =     .5968 

Water  vapor  (steam)     .    .    .    2.25  X  .4805  =  1.0  8  1  1 

Nitrogen 14  X  .2438  =  3.4  1  3  2 

Total  heat  for  1°  F.  5.0  9  1  1 


58  PROPERTIES  OF  GASES  §5 

Then,  since  the  total  heat  evolved  by  burning  1  pound  of 
methane  (marsh  gas)  is  23,513  B.  T.  U.,  the  total  rise  in  the 
temperature  of  the  gaseous  products  of  the  explosion  will  be 

OQ   51^ 

—  =  4,618°  F.;  or,  assuming  an  original  temperature  of 
5.0911 

60°  F.  before  the  explosion,  the  temperature  resulting  from 
the  explosion  is  4,618°  +  60°  =  4,678°  F. 

105.  The  high  temperature  produced  by  the  explosion 
creates  the  expansive  force  of  the  gaseous  products,  the 
absolute  pressure  or  the  tension  of  the  gases  increasing  in 
the  same  ratio  as  the  absolute  temperature;  or,  expressed 
as  atmospheres,  the  total  pressure  created  by  the  explosion 

is,  in  this  case,  =  =  9.88  atmospheres. 


SPONTANEOUS    COMBUSTION 

106.  Spontaneous  combustion  is  said  to  take  place 
when  the  heat  necessary  to  start  the  burning  or  combustion 
is  produced  by  chemical  reaction  originating  within  the  body 
itself.  The  cause  of  the  spontaneous  ignition  of  coal  was 
formerly  thought  to  be  the  oxidation  of  pyrites  contained  in 
it;  it  has  been  learned,  however,  that  this  is  not  the  principal 
cause,  although,  in  the  presence  of  air  and  moisture,  the 
oxidation  of  pyrites,  if  present  in  sufficient  quantity,  may  aid 
in  the  generation  of  heat.  Coal  naturally  absorbs  oxygen 
from  the  air,  undergoing  a  process  of  slow  combustion,  and 
in  so  doing  generates  heat.  The  temperature  attained 
depends  on  the  rapidity  of  the  absorption  of  the  oxygen  and 
the  rate  at  which  the  heat  generated  escapes.  The  former 
fact  is  greatly  influenced  by  the  degree  of  fineness  of  the 
coal  and  the  temperature  of  the  interior  of  the  pile;  and  the 
latter  by  the  size  of  the  heap  and  the  ventilation  of  its 
interior.  The  finer  the  coal,  the  greater  is  the  surface 
exposed  to  the  action  of  the  air,  and  the  absorption  of 
oxygen  becomes  more  energetic  as  the  temperature  is 
increased;  hence,  it  is  evident  that  the  cooler  the  heap  can 
be  kept  and  the  freer  from  fine  coal,  the  less  will  be  the 


§5  PROPERTIES  OF  GASES  59 

danger  of  spontaneous  ignition.  Large  heaps  hold  the  heat 
more  than  small  ones,  and  are  not  so  readily  ventilated. 
While  good  ventilation  cools  the  heap,  very  poor  ventilation 
may  not  allow  sufficient  oxygen  to  enter  the  pile  to  cause 
spontaneous  combustion,  therefore  the  greatest  danger  lies 
midway  between  the  two  conditions. 

Although  the  amount  of  heat  produced  by  the  oxidation  of 
the  pyrites  in  the  .coal  is  small,  this  oxidation  breaks  up  the 
coal  and  thus  presents  fresh  surface  for  the  absorption 
of  oxygen.  __^_ 

PHYSICAL  PROPERTIES  OF  MINE  GASES 

107.  Diffusion  of  Gases. — The  diffusion  of  liquids  is 
an  intermingling  of  the  molecules  of  two  liquids  in  direct 
contact  with  each  other  or  separated  by  a  porous  membrane. 
This  diffusion  or  intermixture  of  the  molecules  is  brought 
about  by  their  power  of  moving  among  each  other,  which 
enables  the  molecules  of  the  two  liquids  to  become  thor- 
oughly intermingled.     The  power  of  diffusion  is  possessed 
by  the  gaseous  molecules  to  the  highest  degree,  and  all  gases 
are  capable  of  perfect  and  comparatively  rapid  intermixture. 
Some  liquids  diffuse  similarly,  though  comparatively  slowly, 
while  others  mix  very  imperfectly,  if  at  all. 

108.  The   diffusion  of   gases   should   not   be   confused 
with   mixtures   by   mechanical    force    or   by    the    action    of 
gravity,  although  mixtures  produced  in  this  way  assist  in  the 
diffusion  of  gases,  and  cause  it  to  take  place  more  rapidly  as 
fresh  surfaces  of  the  different  gases  are  constantly  brought 
together    and    diffusion    thereby   promoted.     For   example, 
when  methane  (marsh  gas)   issues  from  the  floor  of   mine 
workings,  the  gas  being  lighter  than  air  has  a  natural  tend- 
ency to  rise.     The  upward  motion  of  the  gas  assists  its  dis- 
tribution in  the  air  and  promotes  its  diffusion.     On  the  other 
hand,  when  this  gas  issues  from  a  feeder  in  the  roof  of  the 
workings,  it  forms  a  thin  layer  at  the  roof,  except  as  it  may 
be  disturbed  by  the  air-current.     In  this  case,  the  diffusion 
of  the  gas  is  less  rapid  owing  to  its  slower  distribution  in  the 


60  PROPERTIES  OF  GASES  §5 

air.  In  like  manner,  when  carbon  dioxide  (carbonic-acid 
gas)  CO,  issues  from  the  roof,  this  gas  being  heavier  than 
air  tends  to  fall,  and  its  distribution  is  more  complete  and  its 
diffusion  more  rapid  than  when  this  gas  issues  from  the  floor 
of  the  workings. 

109.  Rate  of   Diffusion. — The    rate,   or   velocity,    at 
which  diffusion  takes  place  between  air  and  gas,  or  between 
two  bodies  of  different  gases,  has  been  found,  by  experiment, 
to  be  inversely  proportional  to  the  square  root  of  the  den- 
sities or  specific  gravities  of  the  gases.     This  law  relates  to 
the  diffusion  that  takes  place  at  the  surface  of  contact  and 
does  not  allow  for  any  mechanical  mixing  of  gases.    Thus,  if 
a  jar  of  hydrogen  gas  is  connected  with  a  jar  of  ogygen  gas 
diffusion  will  at  once  begin,  a  portion  of  the  hydrogen  gas 
passing  over  into  the  oxygen,  while  a  portion  of  the  oxygen 
passes  over  into  the  hydrogen.    The  density  of  hydrogen  is  1, 
and  that  of  oxygen  is  16;  that  is,  their  densities  are  as  1  :  16. 
It  is  found  that  for  every  volume  of  oxygen  that  passes  into 
the  hydrogen  there  are  four  volumes  of  hydrogen  passing 
into  the  oxygen,  and,  therefore,  the  rate  of  the  diffusion  of 
the  hydrogen  is  four  times  the  rate  of  the  diffusion  of  the 
oxygen.     In  like  manner,  all  gases  diffuse  into  each  other  in 
the  inverse  ratio  of  the  square  roots  of  their  densities. 

110.  Table  XIV  gives  the  density  or  specific  gravity, 
the  square  root  of  the  density,   and  its  reciprocal,   which 
expresses  the  relative  velocity  of  diffusion,  for  each  of  the 
common  mine  gases,  referred  to  air  as  unity. 

The  table  also  shows  the  relative  velocity  of  diffusion  for 
each  gas  into  air,  as  determined  by  experiment.  It  will  be 
observed  that  the  velocity  of  diffusion,  as  determined  by 
experiment,  in  each  case  agrees  very  closely  with  the  cal- 
culated velocity. 

111.  Occlusion  of  Gases. — A  gas  is  occluded  (hidden) 
when  it  exists  in  the  pores  of  a  solid  substance.     A  familiar 
example  of  the  occlusion  of  gases  is  found  in  the  coal  seams, 
where  gases  often  exist  in  large  quantities  and  are  a  source 
of  danger  in  mining. 


§5 


PROPERTIES  OF  GASES 
TABLE  XIV 


61 


Gas 

Density, 
or 
Specific 
Gravity 

Square 
Root  of 
Density 

Velocity  of  Dif- 
fusion 

Calcu- 
lated 

Deter- 
mined by 
Experi- 
ment 

A/Density 

Hydrogen    

.0693 
•5590 
.9670 
.9700 

•9713 
I.OOOO 

1.1057 

1.1912 

1.5291 

.2632 
•7477 
.9834 
.9849 

.9855 

I.OOOO 

1.0515 
1.0914 
1.2366 

3.7987 
1-3375 
1.0169 
1.0154 
1.0147 
I.OOOO 

.9510 
.9163 
.8087 

3.830 

1.344 
I.OI5 
1.019 
1.014 

•949 
•950 
.812 

Methane  (marsh  gas)   .    . 
Carbon  monoxide  .... 
Ethylene  (olefiant  gas)     . 
Nitrogen      

Air        

Oxveren 

Hydrogen  sulphide   .    .    . 
Carbon  dioxide  . 

The  conditions  that  have  held  these  gases  in  the  coal  and 
adjoining  strata,  till  set  free  by  the  penetration  of  mine  work- 
ings, are  largely  a  close  coal  and  an  impervious  roof  and 
floor.  The  kind  and  amount  of  gases  occluded  in  different 
coal  seams,  and  even  in  different  parts  of  the  same  seams, 
vary  much. 

The  gases  most  commonly  occluded  in  coal  seams  are 
methane  (marsh  gas),  nitrogen,  carbon  dioxide  (carbonic 
acid),  and  traces  of  oxygen,  carbon  monoxide  (carbonic 
oxide),  e'thylene  (olefiant  gas),  and  some  other  hydrocarbons. 

The  relative  percentages  of  these  gases  vary  largely  in 
different  localities,  even  in  freshly  mined  coals. 

112.  Pressure  of  Occluded  Gases. — The  pressure  of 
occluded  gases  has  been  shown,  by  a  number  of  experiments 
in  England,  France,  and  Belgium,  to  often  reach  as  high 
as  150  or  250  pounds  per  square  inch;  and,  in  excep- 
tional cases,  pressures  were  recorded  varying  between  400 
and  500  pounds  per  square  inch.  Whatever  degree  of  exact- 
ness these  experiments  may  have,  they  serve  to  show, 


PROPERTIES  OF  GASES 


§5 


at  least,  the  enormous  pressures  under  which  occluded  gases 
may  be  projected  from  a  newly  exposed  face  of  coal.  This 
pressure  is  often  manifested  by  a  sharp  cracking  and  hissing 
sound  caused  by  the  escaping  gas,  the  splintered  coal  at 
times  being  thrown  with  considerable  violence  into  the  face 
of  the  miner.  The  gases  occupying  the  pores,  or  capillary 
tubes  or  openings  in  the  coal,  are  driven  by  this  pressure 
into  the  cracks  and  crevices  and  larger  openings  in  the  seam, 
from  which  they  flow  in  a  continuous  stream  into  the  atmos- 
phere of  the  mine;  or,  these  gases  may  exude  directly  from 
the  pores  or  capillary  openings  into  the  mine  atmosphere 
wherever  a  fresh  face  of  coal  is  exposed. 

TABLE  XV 


Gas 

Relative  Velocity  of 
Transpiration 

Hydrogen 

2  066 

Olefiant  gas     

1.788 

Marsh  gas                                                  .    . 

6^Q 

Hydrogen  sulphide    

.458 

Carbon  dioxide           .            .            . 

217 

Carbon  monoxide      

.014 

Nitrogen      .    .            .        ... 

O1O 

Air        

.OOO 

Oxygen                        .... 

QO1 

113.  Transpiration  of  Gases  Prom  Coal. — The  term 
transpiration,  as  here  used,  relates  to  the  more  or  less  steady 
outflow  of  occluded  gases  from  the  pores  of  the  coal.  It  has 
been  found  by  numerous  experiments  that  the  velocity  of 
transpiration,  like  the  velocity  of  diffusion,  is  different  for 
different  gases  subjected  to  the  same  pressure.  The  velocity 
of  transpiration,  however,  follows  a  different  law  from  that 
of  diffusion.  Table  XV  gives  the  relative  velocity  of  trans- 
piration for  each  of  the  common  mine  gases  as  obtained 
from  Graham's  experiments. 


§5  PROPERTIES  OF  GASES  63 

It  will  be  observed  that  the  velocity  of  transpiration, 
unlike  that  of  diffusion,  is  independent  of  the  density  of 
the  gas. 

114.  Effect  of  Rate  of  Transpiration. — The  rate  of 
transpiration  of  the  different  gases  occluded  in  the  coal  has 
an  important  effect  in  determining  the  character  of  the  gaseous 
mixtures  issuing  from  the  seam  and  the  gaseous  condition 
of  the  mine  workings.     The  more  rapid  transpiration  of  the 
hydrocarbon  gases,  as  methane  (marsh  gas)   and  ethylene 
(ethylene  or  blefiant  gas),  tends  to  increase  the  percentage  of 
these  gases  in  the  mine  air;  while  the  percentage  of  carbon 
dioxide  (carbonic  acid)  and  nitrogen,  which  are  always  pres- 
ent to  some  extent  in  the  coal,  is  decreased  by  the  same 
cause.     Owing  to  this  difference  in  the  rate  of  transpiration 
of  the  gases,  .it  has  been  a  difficult  matter  to  determine,  with 
accuracy,  the  percentage  of  different  gases  in  different  coals. 
The  results  of  a  large  number  of  analyses,  however,  show 
that  the  principal  occluded  gases  are  methane  (marsh  gas), 
nitrogen  and  carbon  dioxide  (carbonic  acid).    In  some  coals, 
methane  has  been  shown  to  form  93  per  cent,  of  the  occluded 
gases  of  the  coal;  in  other  coals,  nitrogen  gas  has  formed 
91  per  cent,  of  these  gases;  while  in  still  other  coals,  carbon 
dioxide  (carbonic-acid  gas)  has  formed  54  per  cent.     Oxygen 
rarely  exceeds  4  or  5  per  cent,  of  the  occluded  gases  of  coal, 
and  is  usually  much  less. 

115.  Feeders    and    Blowers. — Wherever    a    cavity, 
crevice,  or  fissure  exists  in  proximity  to  or  in  connection 
with  a  gaseous  seam,  it  becomes  charged  with  the  occluded 
gases  of  the  seam,  under  the  same  pressure.     A  dangerous 
reservoir  of  gas  is  thus  formed,  which  may  at  any  moment 
be  pierced  or  tapped  by  the  drill  of  the  miner,  or  find  vent 
into  the  mine  workings  through  a  crack  or  crevice.     Such 
cavities,  crevices,  or  fissures  charged  with  gas  are  termed 
feeders,  and,  when  tapped,  the  stream  of  gas  issuing  is  called 
a  blower.     A  blower  may  continue   to  discharge   gas  for  a 
length  of  time  depending  on   the   size  of  the  blower,   the 
size  of  the  feeders,  and  the  area  drained  thereby. 


64 


PROPERTIES  OF  GASES 


§5 


116.  Outbursts.  —  In  working  coal  seams  in  some  local- 
ities, the  presence  of  occluded  gases  is  frequently  mani- 
fested by  a  violent  outburst  at  the  working  face.  These 
outbursts  often  take  place  without  warning  and  produce  an 
effect  similar  to  that  of  an  explosion,  throwing  down  the  coal 
in  large  quantities. 

The  cause  is  a  feeder  of  gas  finding  access  to  a  more  or 
less  vertical  crevice  or  cleat  behind  the  working  face  of  the 
coal.  Its  pressure  thus  becomes  distributed  over  a  consid- 
erable area  of  coal,  and  exerts  a  powerful  localized  force. 

Fig.  11  represents  a  dangerous  pocket  of  gas  lying 
beneath  an  impervious  stratum  of  close-grained  rock,  which 


has  prevented  its  escape.  The  gas  is  under  enormous  pres- 
sure, incident  to  the  great  weight  of  the  overlying  strata. 
The  cleats  or  vertical  fissures  shown  in  the  coal  seam  are 
"face  cleats,"  the  entry  or  gangway  being  driven  "end  on." 
The  pressure  of  the  gas  causes  the  foliated  roof  shale  to  rest 
heavily  on  the  timbers,  and  finally  breaks  the  shale,  thus 
opening  a  communication  for  the  gas  with  the  cleats  of 
the  coal.  The  pressure  of  the  gas  is  thereby  distributed 
over  a  large  area,  often  throwing  down  tons  of  coal  or 
shale  with  the  force  of  an  explosion. 

There  are  well-authenticated,  although  seemingly  incredi- 
ble, cases  on  record  where  headings  and  chutes  have  been 
completely  blocked  by  a  compacted  mass  of  from  15  to  20 
tons  of  fine  coal,  thus  thrown  from  the  face  without  the 


§5  PROPERTIES  OF  GASES  65 

slightest  warning.  In  other  instances,  the  outburst  may  be 
accompanied  by  a  subterranean  pounding,  or  "bumping,"  as 
the  miners  term  it,  or  by  a  sudden  report,  similar  to  that  of 
a  blast.  This  pounding,  or  "bumping,"  sometimes  continues 
at  intervals  for  2  or  3  days  prior  to  the  outburst.  By  far  the 
larger  number  of  violent  outbursts  are  of  methane  (marsh 
gas);  although  instances  are  recorded  of  very  violent  out- 
bursts of  carbon  dioxide  (carbonic-acid  gas). 


GOB  FIRES 

117.  A  gob  fire  is  a  fire  occurring  in  the  gob  or  waste 
material  produced  in  mining  coal  and  left  underground. 
The  gob  consists  of  rock,  slate,  bony  coal,  which  is  more 
or  less  combustible,  and  also  a  considerable  amount  of  fine 
coal  or  slack.  The  moist  condition  of  the  mine  workings 
assists  the  slow  combustion  of  the  fine  coal  and  slack  and 
not  infrequently  sufficient  heat  is  developed  in  the  mass  to 
produce  the  spontaneous  combustion  of  the  coal,  or  the 
woody  material  with  which  it  may  be  in  contact.  The  gas 
produced  by  the  incomplete  combustion  of  the  carbon  is 
largely  carbon  monoxide  CO,  which  is  combustible  and 
which  therefore  assists  in  spreading  the  fire. 

Gob  fires  occur  more  frequently  under  moist  conditions 
and  where  the  ventilation  is  sluggish.  Some  coals,  more 
highly  inflammable  than  others,  are  particularly  subject  to 
spontaneous  combustion,  and  gob  fires  occur  more  fre- 
quently in  mines  producing  such  coals.  Gob  fires  are  often 
a  menace  to  the  mine  on  account  of  the  noxious  gases  given 
off  and  because  the  fire  may  extend  to  the  unmined  coal. 
If  gas  feeders  occur  in  the  floor  of  the  workings,  the  gas  is 
often  fired  by  the  heat  of  the  combustion  in  the  gob,  and  the 
flame  travels  back  in  the  waste,  where  it  continues  to  burn, 
often  resisting  all  efforts  to  extinguish  it. 


TREATMENT    OF    GOB    FIRES 

118.     The    first   indications  of   fire    in    the    gob   should 
receive  prompt  attention,   as   any  delay  can  only  result  in 

increasing  the  danger  and  difficulty  to  be  encountered  in  the 

i  :,    i; 


66*  PROPERTIES  OF  GASES  §5 

treatment  of  the  fire.  The  method  of  treatment  will  depend 
on  the  stage  of  progress  of  the  fire,  and  may  be  described 
as  follows. 

119.  Loading  Out. — If  the  fire  is  a  small  one  and  is  so 
located  that  it  can  be  reached  by  cars  or  barrows,  all  the  hot 
material  undergoing  slow  combustion  should  be  loaded  into 
cars  and  taken  to  the  surface,  and  no  trace  of  fire  allowed  to 
remain;  no  water  should  be  used  in  this  case,  as  the  addition 
of  moisture  tends  to  increase  the  difficulty.     The  locality 
should  then  be  thoroughly  ventilated  by  a  good  current  of 
pure  air,  to  remove  as  far  as  possible  the  gases  that  still 
remain  in  the  gob,  and  to  reduce  the  temperature  of  the 
mine   by   carrying   away  the   heat    generated   by  the  slow 
combustion.     By  this  means,   the  conditions    favoring    the 
combustion  are  gradually  removed. 

120.  Exploding  Dynamite. — When  gas  feeders  have 
become  ignited  by  a  gob  fire  or  by  the  flame   of  a  blast  or 
otherwise,  and  the  flame  has  traveled  back  through  the  gob, 
it  may  often  be  extinguished  by  the  explosion  of  a  small 
portion  of   a  stick  of   dynamite  close    to    the   place.     The 
concussion  produced  by  the  explosion  of  the  dynamite  will 
often  extinguish  the  flame  of  the  burning   gas  when  other 
means  have  failed. 

121.  Sealing  Off  With  Stoppings. — If  fire  has  pene- 
trated into  the  gob  to  such  an  extent  that  the  method  of 
loading  out  the  material  is  impracticable,  owing  to  the  large 
amount  of  waste  material  to  be  handled,  the  section  of  the 
mine  in  which  the  fire  is  located  must  be  isolated  by  stop- 
pings built  at  the  mouth  of  the  room  or  rooms  if  the  fire  is 
local,  or  at  all  points  leading  to  the  affected  section  of  the 
mine  if  it  is  more  general.     The  work  of  building  these  stop- 
pings must  be  commenced  at  the  return  end  of  the  district, 
and  proceed  in  order  toward  the  intake,  the  stopping  at  the 
intake  end  being  closed  last,  in  order  to  avoid  a  dangerous 
accumulation  of  explosive  gas,  which  might  result  in  a  serious 
explosion  if  the  stopping  were  built  in  the  reverse  order. 
The  stoppings  are  built  of  brick  laid  in  fireclay,  or  of  concrete, 


§5  PROPERTIES  OF  GASES  67 

and  should  be  well  sealed  to  prevent  air  reaching  the  fire. 
Tubes  or  pipes  should  be  built  in  the  first  and  last  stop- 
pings or  at  other  suitable  points,  to  afford  the  means  of 
testing,  from  time  to  time,  the  gas  coming  from  the  enclosed 
space;  these  pipes  should  be  tightly  closed  with  plugs. 

122.  Sealing  Off  With  Culm.— Instead  of    brick  or 
concrete  stoppings,  culm  is  often  used  very  successfully  for 
closing   off  a  mine.  fire.     The   culm   mixed   with   water   is 
run  Into  the  mine  through  pipes,  just  as  is  done  when  the 
workings  are  flushed  with  culm  to  support  the  top  so  that 
the  pillars  may  be  removed.     In  this  way,  a  practically  air- 
tight barrier  is  made  around  the  fire,  which  barrier  is  allowed 
to  remain  until  all  the  fire  dies  out  through  lack  of  oxygen  to 
support  it.     The  culm  is  then  loaded  out  if  it  is  desired  to 
get  at  the  place  where  the  fire  was;  or,  if  it  is  not  necessary 
to  reach  the  place,  the  culm  is  allowed  to  remain  and  thus 
prevents  any  recurrence  of  the  fire. 

123.  Flooding. — The  flooding  of  a  mine  or  any  portion 
of  it,  for  the  purpose  of  extinguishing  a  mine  fire,  should 
only  be  employed  as  a  last  resort.     The  enforced  idleness  of 
the  mine,  or  any  portion  of  it,  and  the  damage  caused  by  the 
water,  together  with  the  expense  of  pumping  out  the  water 
when  the  fire  is  extinguished,  are  sufficient  reasons  why  this 
means  should  not  be  employed  till  other  methods  have  failed 
or  been  proved  impracticable.     Where  flooding  is  necessary, 
substantial  dams  are  built  across  the  openings  leading  to  the 
section  of  the  mine  where  the  fire  is  located.     The  dam 
should  be  located  so  as  tp  reduce  the  area  of  the  workings 
to  be  flooded  to  a  minimum.     The  flooding  may  be  accom- 
plished from  an  opening  connected  with  the  workings,  or 
through  a  bore  hole  sunk  from  the  surface.     The  water  may 
be  pumped  or  drained  into  the  workings.     A  sufficient  length 
of  time  is  allowed  for  the  water  to  penetrate  all  portions  of 
the  affected  area. 

124.  When  a  sufficient  time  has  elapsed  for  the  extin- 
guishment of  the  fire,  which  should  not  be  less  than  a  month 
or  6  weeks,  and  sometimes  longer,  according  to  the  size  of 


68  PROPERTIES  OF  GASES  §5 

the  fire  and  the  area  flooded,  the  water  is  drained  or  pumped 
from  the  workings,  which  are  then  ventilated  and  dried  by  a 
strong  current  of  pure  air.  The  work  of  opening  a  flooded 
section  of  a  mine  should  proceed  with  caution,  the  return 
stoppings  being  taken  down  first,  and  afterwards  the  stop- 
pings at  the  intake  end  of  the  district.  As  early  as  possible, 
an  examination  should  be  made  of  the  flooded  area,  to  ascer- 
tain if  the  fire  has  been  thoroughly  extinguished.  The  dry- 
ing of  the  workings  should  be  accomplished  as  quicky  as 
possible,  and  a  careful  watch  kept  for  any  evidences  of  heat 
in  the  gob.  Safety  lamps  should  always  be  used  when 
entering  an  area  that  has  been  closed  for  any  length  of  time, 
and  a  careful  test  made  for  any  accumulations  of  gas. 


MINE  GASES 


OCCURRENCE,  PROPERTIES,  BEHAVIOR, 
AND  DETECTION   OF  MINE   GASES 


GASES   COMMON  TO  MINES 

1.  The  gases  met  with  in  mines  are  comparatively  few  in 
number,  but  a  thorough  knowledge  of  their  occurrence,  prop- 
erties, behavior,  and  the  manner  of  their  detection  is  impor- 
tant. In  Table  I  are  given  the  names,  chemical  symbols, 
and  specific  gravities  of  the  gases  most  commonly  occurring 
in  mines,  considered  in  the  order  of  their  importance. 

TABLE  I 


Gas 


Marsh  gas  (methane,  or  carbureted  hydro- 
gen)   

Carbon  monoxide,  carbonic  oxide  (white- 
damp)  

Carbon  dioxide,  carbonic-acid  gas  (black- 
damp,  or  chokedamp) 

Hydrogen  sulphide,  sulphureted  hydrogen 
(stinkdamp) 

Olefiant  gas  (ethene,  or  ethylene)  .    .    .    . 

Nitrous  oxide  (laughing  gas) 

Nitrogen 

Oxygen    

Hydrogen 


Symbol 


CO 
CO, 


NtO 
N 
O 
H 


Specific 
Gravity 
(Air=  i) 


•559 

.967 

1.529 

1. 175 
•973 

1.525 
.971 

1. 1 06 
.069 


Copyrighted  by  International  Textbook  Company.    Entered  at  Stationers'  Hall.  London 


2  MINE  GASES  §6 

2.  Marsh  Gas  (Methane,  or  Carbureted  Hydrogen, 

CH^). — Marsh  gas  issues  from  the  coal,  being  one  of  the 
gases  occluded,  or  imprisoned,  in  coal  during  its  formation. 
It  was  produced  by  the  gradual  change  that  converted 
vegetable  matter  into  coal,  wherever  this  has  taken  place 
with  the  exclusion  of  air  and  under  water.  Marsh  gas  is  a 
colorless,  odorless,  and  tasteless  gas  having  a  specific  gravity 
of  .559.  It  diffuses  rapidly  in  the  air,  forming  an  explosive 
mixture.  The  gas  is  not  poisonous,  and  when  mixed  with 
air  in  sufficient  proportion  a  person  may  breathe  it  with 
impunity  for  a  considerable  time,  suffering  only  a  slight 
dizziness,  which  passes  off  when  the  person  returns  to  fresh 
air.  Pure  marsh  gas  will  not  support  life,  but  suffocates  by 
excluding  oxygen  from  the  lungs.  It  is  combustible  and 
burns  with  a  blue  flame,  but  will  not  support  combustion; 
that  is,  unmixed  with  air,  it  extinguishes  the  flame  of  a  lamp. 
Being  lighter  than  air,  this  gas  accumulates  at  the  roof  and 
in  the  higher  portions  of  the  mine  workings,  except  when 
removed  by  the  ventilating  current.  The  presence  of  marsh 
gas  in  mine  air  is  detected  by  its  effect  on  the  flame  of  a 
safety  lamp.  When  present  in  sufficient  quantity,  it  produces 
a  flame  cap,  the  height  of  which  increases  with  the  percentage 
of  gas  present. 

3.  Carbon    Monoxide,    Whltedamp,    or    Carbonic 
Oxide,    CO. — Carbon    monoxide   occurs   in   the   coal   as   an 
occluded    gas    to   a    limited   extent  only.     Its   chief   source 
of  production  in  the  mine  is  the  slow  combustion  of  carbo- 
naceous matter  in  a  limited  supply  of  air;  it  is  one  of  the 
chief  products  of  gob  fires,  and  is  also  produced  largely  in 
the  imperfect  explosion  of  blasting  powder.     In  mine  explo- 
sions, it  may  be  produced  in  large  quantities  by  the  reaction 
of  incandescent  carbon  or  soot  on  carbon  dioxide  (carbonic- 
acid  gas).     It  is  an  odorless,  colorless,  and  tasteless  gas 
having  a  specific  gravity  of  .967;  its  diffusion  in  the  mine  air 
is  not  so  rapid  as  that  of  marsh  gas  (methane);  it  is  com- 
bustible, burning  with  a  pale  blue  flame,  but,  by  itself,  does 
not  support  combustion.     Lamps  burn  more  brightly  in  air 


§6  MINE  GASES  3 

containing  it  than  in  pure  air,  which  fact,  added  to  its  poison- 
ous character,  renders  it  the  most  deadly  and  dangerous  of  all 
mine  gases.  Mixed  with  air,  it  has  the  widest  explosive  range 
of  any  of  the  mine  gases,  except  hydrogen;  its  effect,  when 
present  in  a  firedamp  mixture,  is  to  widen  the  explosive  range 
of  the  firedamp.  Carbon  monoxide,  even  in  small  propor- 
tions, is  extremely  poisonous;  it  combines  with  the  coloring 
matter  of  the  blood  and  prevents  it  from  carrying  oxygen  to 
the  tissues.  It  acts  on  the  human  system  as  a  narcotic,  pro- 
ducing drowsiness  or  stupor,  followed  by  acute  pains  in  the 
head,  back,  and  limbs,  and  afterwards  by  delirium  and  death 
if  relief  is  not  obtained.  Being  lighter  than  air,  this  gas 
accumulates  in  the  roof  and  upper  portions  of  mine  workings, 
except  when  removed  by  the  air-current.  The  presence  of 
this  gas  is  detected  in  the  mine  air  by  its  effect  in  brightening 
and  lengthening  the  flame  of  the  lamp;  the  gas,  when  present 
in  sufficient  quantity,  causes  the  flame  to  reach  upwards  in  a 
slim,  quivering  taper. 

4.  Carbon  Dioxide,  Blackdamp,  or  Carbonic-Acid 
Gas,  CO*. — Carbon  dioxide  always  exists  as  an  occluded 
gas  in  the  coal;  its  chief  source  of  production  in  the  mine, 
however,  is  the  combustion  of  carbonaceous  matter,  whether 
slow  or  rapid,  in  a  plentiful  supply  of  air;  it  is  a  product  of 
the  burning  of  lamps,  breathing  of  men  and  animals,  com- 
bustion of  coal  and  powder,  and  decay  of  timber;  it  is  also 
given  off  in  considerable  quantity  in  the  evaporation  of 
calcareous  mine  water  that  has  been  under  pressure  and 
from  which  the  pressure  has  been  removed.  It  is  a  color- 
less and  odorless  gas  having  a  specific  gravity  of  1.529;  when 
breathed  in  sufficient  quantity,  it  produces  a  distinctly  acid 
taste;  it  diffuses  slowly  in  the  air,  which  increases  the  diffi- 
culty of  its  removal  by  the  ventilating  current.  This  gas  is 
not  combustible  and  does  not  support  combustion.  The 
presence  of  small  quantities  of  the  gas  dims  the  flame  of  the 
lamp;  when  larger  quantities  are  present,  the  flame  is  extin- 
guished. When  present  in  firedamp  mixtures,  its  effect  is 
to  reduce  the  explosive  violence  of  the  mixture.  It  is  not 


4  MINE  GASES  §6 

poisonous,  but  suffocates  by  excluding  oxygen  from  the 
lungs;  when  breathed  for  some  length  of  time,  small  quan- 
tities of  the  gas  cause  headache  and  nausea,  followed  by 
pains  and  weakness  in  the  back  and  limbs;  larger  quantities 
produce  death.  Being  heavier  than  air,  this  gas  accumulates 
at  the  floor  and  in  the  lower  mine  workings,  except  as 
removed  by  the  air-current.  The  presence  of  this  gas  in 
mine  air  is  detected  by.  the  dimness  of  the  lamps,  and  the 
total  extinction  of  the  flame  when  a  large  percentage  of 
the  gas  is  present.  It  is  called  blackdamp  because  it  puts 
out  a  light,  and  chokedamp  because  it  produces  a  choking 
sensation  when  breathed. 

5.  Hydrogen    Sulphide,    Stlnkdamp,    or    Sulphu- 
reted    Hydrogen,    HtS. — Hydrogen   sulphide  is  produced 
in   the  mine  by  the   disintegration   of  pyrites   occurring  in 
the  coal  or  the  underlying  or  overlying  strata.     It  is  pro- 
duced in  smaller  quantities  by  the  explosion  of  powder  and 
the  evaporation  of  mine  water.     It  is  a  colorless  gas  having 
a  disagreeable  taste  and  possessing  a  strong  odor  resembling 
that  of  rotten  eggs;  its  specific  gravity  is  1.175;  it  diffuses 
slowly  into  the  air;  the  gas  is  combustible  but  will  not  sup- 
port combustion.     Mixed  with  seven  times  its  volume  of  air, 
it  forms  a  violently  explosive  mixture. 

It  is  extremely  poisonous,  combining  with  the  coloring 
matter  of  the  blood.  When  breathed  in  small  quantities,  it 
deranges  the  system;  and  in  larger  proportions  produces 
unconsciousness,  prostration,  and  death.  Being  heavier 
than  air,  this  gas  accumulates  at  the  floor  and  in  the  lower 
mine  workings.  The  presence  of  this  gas  is  easily  detected 
by  its  smell. 

6.  Olef lant  Gas,  Ethene,  or  Ethylene,  C,Ht.— Though 
present  in  small  amounts,  olefiant  gas  forms  one  of  the  impor- 
tant gases  occluded  in  coal.     It  is  one  of  the  products  of 
the  formation  of  coal.     It  is  a  colorless  gas  having  a  faint 
odor  resembling  ether;  its  specific  gravity  is  .974;  it  diffuses 
rapidly  in  the  air;  it  is  combustible,  burning  with  a  brilliant 
white  flame,  but  will  not  support  combustion.     Mixed  with 


§6  MINE  GASES  5 

air,  it  is  powerfully  explosive,  requiring  twice  its  volume  of 
oxygen  for  its  complete  combustion.  It  is  not  poisonous; 
in  the  mine  it  is  always  associated  with  marsh  gas  (methane) 
to  a  greater  or  less  extent,  and  possesses  like  properties 
with  this  gas;  it  will  not  support  life  or  flame,  but  is  never 
present  in  sufficient  quantity,  however,  to  produce  suffoca- 
tion. It  is  lighter  than  air,  and  with  marsh  gas  accumulates 
at  the  roof.  In  the  mine,  it  does  not  form  a  distinct  gas; 
its  presence  in  firedamp  mixtures,  however,  is  important,  as 
it  widens  the  explosive  range  and  increases  the  explosive 
force  of  the  firedamp.  The  gas  is  not  easily  detected  in  the 
mine,  but  its  presence  is  manifested  by  the  more  active 
behavior  of  the  flame  and  the  tendency  of  the  lamp  to  fill 
with  flame  almost  before  a  cap  is  observed.  Olefiant  gas 
produces  very  much  the  same  effect  on  the  lamp  as  is  pro- 
duced by  marsh  gas. 

7.  Nitrous  Oxide,  N,O. — This  gas,  commonly  known 
as  laughing  gas,  and  often  employed  by  dentists  to  produce 
unconsciousness,   frequently   forms    one   of   the  constituent 
gases  of  the  afterdamp  produced  in  a  mine  explosion.     It  is  a 
colorless   and  odorless  gas  having  a  distinctly  sweet  taste 
and  a  specific  gravity  of  1.525;    it  diffuses  slowly  in  the  air; 
it    supports    combustion    with    almost    as    great    energy   as 
oxygen.     When  breathed,  the  gas  quickly  produces  uncon- 
sciousness;   it  is  not,   however,   a   poisonous   gas,   and  its 
narcotic  effect  is  only  of  short  duration.     Owing  to  the  fact 
that  lamps  burn  freely   in   this  gas,   its  presence   in  after- 
damp,  like  that  of  carbon  monoxide    (carbonic  oxide),   is 
unsuspected  except  by  the  effect  produced  on  the  system. 
The  gas  is  heavier  than  air,  its  density  being  almost  equal 
to  that  of  carbon  dioxide  (carbonic-acid)  gas. 

8.  Nitrogen,  N. — Nitrogen  occurs  as  an  occluded  gas  in 
coal  in  widely  varying  proportions.     On  the  average  it  is 
probably  below  10  per  cent.,  but  it  has  been  found  to  con- 
stitute as  much  as  95  per  cent,  of  the  gas  from  pockets  in 
some  localities.     One  of  the  chief  sources  of  nitrogen,  how- 
ever, is  the  atmosphere,  of  which  it  forms  about  80  per  cent., 


6  MINE  GASES  §6 

or  four-fifths,  by  volume,  and  about  75  per  cent.,  or  three- 
fourths,  by  weight.  As  the  oxygen  of  the  air-current  is  con- 
sumed, in  its  passage  through  the  mine,  by  the  various  forms 
of  combustion,  the  percentage  of  nitrogen  remaining  in  the  air 
is  greatly  increased.  Nitrogen  is  a  colorless,  odorless,  and 
tasteless  gas,  and  has  a  specific  gravity  of  .971;  it  is  not  com- 
bustible and  will  not  support  combustion;  it  is  not  poisonous, 
but  suffocates  by  excluding  oxygen  from  the  lungs  in  the  same 
manner  as  carbon  dioxide.  It  is  lighter  than  air,  and  when 
present  in  large  quantities  should  be  found  at  the  roof  of  the 
mine  workings;  it  is  distinguished  in  the  mine  from  carbon 
dioxide  by  its  lower  density,  carbon  dioxide  collecting  at 
the  floor  and  nitrogen  at  the  roof.  The  effect  of  nitrogen 
is  to  dim  the  flame  of  the  lamp  and  to  extinguish  it  when 
present  in  sufficient  quantity. 

9.  Oxygen,  O. — Oxygen  is    the    greatest    supporter    of 
animal  life  and  combustion;  it  exists  in  very  minute  quanti- 
ties as  an  occluded  gas  in  some  coals;  its  chief  source,  how- 
ever, is  the  atmosphere,  of  which  it  forms  20.7  per  cent,  by 
volume,  or  practically  one-fifth.     It  is  a  colorless,  odorless, 
non-poisonous,  and  tasteless  gas  somewhat  heavier  than  air 
and  has  a  specific  gravity  of  1.106.     When  present  in  excess 
in  the  atmosphere  it  produces  an  exhilarating  effect  on  the 
system,  increasing  the  circulation  of  the  blood. 

10.  Hydrogen,  H. — The  occurrence  of  free  hydrogen  in 
mines  is  very  rare;  it  is  produced  in  the  afterdamp  of  some 
mine  explosions^   particularly  when   the    firedamp   mixture 
contains  more  than  9.5  per  cent,   of  marsh  gas — in  other 
words,  when  the  percentage  of  marsh  gas  (methane)  in  the 
firedamp  is  in  excess  of  that  required  to  produce  a  maximum 
explosive    force.     Hydrogen    is    a   colorless,   odorless,   and 
tasteless  gas,  having  a  specific  gravity  of  .069,  and  diffuses 
with  great  rapidity  in  the  air,  being  the  lightest  gas  known. 
It  is  not  uncommon  for  miners  to  mistake  marsh  gas,  or 
carbureted  hydrogen,  for  hydrogen. 


§6  MINE  GASES  7 

MIXTURES   OF  MINE   GASES 

11.  The  several  mine   gases  described  rarely  occur  in 
mines  in  a  pure  state,  or  unmixed  with  air  or  other  gases. 
The  kinds  and  proportions  of  the  gases  found  in  different 
mines  vary   greatly.     Not   only    is  the  composition  of  the 
gaseous  mixture  given  off  from  different  coals  quite  vari- 
able, but  the  mixture  of  gases  issuing  from  the  coal  is  con- 
stantly being  varied  by  mixing  with  air  and  by  the  various 
processes  of  oxidation  continually  taking  place  in  the  mine, 
producing  frequently  quite  complex  and  varying  mixtures. 
The  nature  of  these  gaseous  mixtures  is  determined  by  the 
kinds  and  proportions  of  the  several  gases  of  which  they  are 
composed.     The  gases  are  mechanically  mixed  and  have  no 
chemical  effect  on  each  other,  except  as  they  combine  owing 
to  a  rise  of  temperature.     The  various  forms  of  oxidation 
that  are    continually  taking   place  in  the  mine  consume  a 
portion  of  the  oxygen  of  the  mine  air,  leaving  the  remain- 
ing atmosphere  poor  in  oxygen  and  containing  an  excess  of 
nitrogen  and  a  considerable  percentage  of  carbon  dioxide. 

12.  Firedamp. — In  American  practice,  the  term  fire- 
damp   relates    to    any  explosive    mixture    of    marsh    gas 
(methane)  and  air,  together  with  such  other  gases  as  may 
be  associated  with   marsh    gas.     In  *  England,  firedamp   is 
another  name  for  marsh  gas  and  its  associated  gases.     The 
explosive  character  of  any  gas  is  only  developed  when  the 
gas  is  mixed  with  air  in  certain  proportions.     The  maximum 
explosive  force  is  developed  when  the  proportion  of  air  is 
such  as  is  required  for  the  complete  combustion  of  the  gas. 
Too  little  air  results  in  a  partial  combustion  of  the  gas  and 
reduces  the  force  of  the  explosion;  too  much  air  dilutes  the 
gas  and  also  lessens  the  force  of  the  explosion.    The  reaction 
that  takes  place  and  the  gaseous  products  of  the  explosion 
also  vary  with  the  proportion  of  air  in  the  mixture. 

13.  Pure  marsh  gas  will  extinguish  the  flame  of  a  lamp, 
but  the  flame  will  burn  in  a  mixture  of  this  gas  with  a  suffi- 
cient quantity  of  air.     If  an  increasing  proportion  of  air  is 


8 


MINE  GASES 


§6 


added  to  pure  marsh  gas,  the  effect  is  manifested  by  an 
increased  disturbance  of  the  flame  of  a  lamp,  and  the  mix- 
ture begins  to  be  explosive  when  the  proportion  of  marsh 
gas  to  air  is  1  to  5,  which  is  called  the  lower  explosive 
limit.  The  maximum  explosive  force  is  developed  when  the 
proportion  of  gas  to  air  is  1  to  9.66;  and  the  mixture  ceases 
to  be  explosive  when  the  proportion  of  gas  to  air  is  1  to  13, 
which  is  called  the  higher  explosive  limit. 

Table  II  expresses  the  proportion  of  gas  to  air,  and  the 
percentage  of  gas  in  the  mixture  for  firedamp,  at  its  lower 
explosive  limit,  its  maximum  explosive  point,  and  its  higher 

explosive  limit. 

TABLE  II 


Explosive  Range 

Proportion  of  Gas 
to  Air 

Percentage  of 
Marsh  Gas 
in  the  Firedamp 
Mixture 

Gas 

Volumes 

Air 
Volumes 

Lower  explosive  limit     .    . 
Maximum  explosive  point 
Higher  explosive  limit    .    . 

I 
I 
I 

5.00 
9.66 
13.00 

20.0O 
9.38 
7.14 

14.  A  more  or  less  definite  mixture  of  marsh  gas  with 
carbon  dioxide  is  often  found  in  mine  workings  generating 
both  of  these  gases.  The  name  flashdamp  has  been  pro- 
posed for  this  mixture,  for  the  reason  that  it  is  difficult  to 
observe  the  flame  cap  produced  by  it  in  the  Davy  lamp  owing 
to  its  short  duration.  The  mixture  to  which  this  name  has 
been  given  contains  sufficient  carbon  dioxide  to  render  it 
inexplosive.  When  a  safety  lamp  containing  fresh  air  within 
the  gauze  is  raised  quickly  into  the  mixture,  a  flame  cap 
appears  for  a  moment,  but  passes  away  as  quickly  as  the 
mixed  gases  enter  the  lamp,  the  flame  also  growing  dim  and 
often  dying  out.  When  the  mixture  contains  more  marsh  gas 
than  it  does  carbon  dioxide,  it  is  lighter  than  air  and  is  found 
near  the  roof;  when  it  contains  more  carbon  dioxide  than 
marsh  gas,  it  is  heavier  than  air  and  is  found  near  the  floor. 


§6  MINE  GASES  9 

15.  Effect  of  Other  Gases  and  Dust  on  Firedamp. 

The  effect  of  the  presence  of  other  gases  is  to  narrow  or 
widen  the  explosive  range  of  the  firedamp  according  to  the 
kind  and  amount  of  the  gases  present. 

1.  Carbon  dioxide  (carbonic-acid gas) ,  CO3,  mixed  with  fire- 
damp makes  the  mixture  less  explosive,  or,  in  other  words, 
narrows  the  explosive  range  of  the  firedamp.     The  addition 
of  one-seventh  of  its  volume  of  carbon  dioxide,  CO3,  to  a 
mixture  of  firedamp  at  its  most  explosive  point,  renders  the 
firedamp  inexplosive. 

2.  Carbon  monoxide  {carbonic  oxide]  mixed  with  firedamp 
widens  the  explosive  range  of  the  firedamp,  thereby  making 
mixtures  explosive  that  would  not  otherwise  be  explosive. 

3.  Olefiant  gas   (ethylene),  C//"4,   in  a  firedamp  mixture 
renders  it  more  easily  ignitible;  this  gas  also  increases  the 
explosive  force  of  the  mixture. 

4.  Coal  dust  suspended  in  the  air  widens  the  explosive 
range  in  the  same  manner  as  does  carbon  monoxide.     Under 
the  influence  of  flame,  carbon  monoxide,  CO,  is  formed  by 
the  partial  combustion  of  the  coal  dust  suspended  in  the  air. 

5.  Nitrogen  in  a  firedamp  weakens  the  explosive  force  of 
the  mixture  by  the  dilution  of  the  gas,  the  nitrogen  being 
inert.     The    addition   of  one-sixth  of  its  volume    of   nitro- 
gen to  a  mixture  of  firedamp  at  its  most  explosive  point, 
renders  the  mixture  inexplosive. 

16.  Effect  of  Pressure  and  Temperature  on  Fire- 
damp.— An  increase  of  pressure  raises  the  temperature  of 
ignition  of  any  combustible  gas.     When  firedamp  is  exploded 
under  an  increased  pressure,  not  only  is  the  temperature  of 
the  explosion  raised,  but  the  explosive  force  is  very  much 
increased.     The    volume    and    intensity    of    the    flame    are 
important  factors  in  maintaining  the  combustion  of  a  body  of 
gas.     The  larger  the  volume  of  flame,  the  greater  is  the 
amount  of  heat  developed,  which  overcomes  the  cooling  of 
the  gases  and  extinction  of  the  flame  due  to  the  lower  tem- 
perature of  the  surfaces  in  contact  with  the  gas.     This  is 
illustrated  by  the  fact  that  a  mixture  of  one  part  of  marsh 


10  MINE  GASES  §6 

gas  with  thirteen  parts  of  air  will  not  explode  in  a  glass 
tube  f  inch  in  diameter,  while  a  mixture  of  one  part  of  gas 
to  twelve  of  air  fails  to  explode  in  a  tube  i  inch  in  diameter, 
due  in  each  case,  to  the  cooling  effect  of  the  tube  on  the 
smaller  volume  of  gas  passing  through  it. 

The  size  of  the  openings  in  a  mine  also  exerts  a  similar 
effect  on  the  ignition  and  explosion  of  accumulated  bodies  of 
gas.  This  would  indicate,  to  a  certain  degree  at  least,  that 
the  ignition  of  a  body  of  gas  is  more  difficult,  or  requires  a 
larger  volume  or  higher  temperature  of  flame,  or  both,  in 
narrow  contracted  openings  than  in  larger  openings.  What- 
ever decreases  the  temperature  of  gases  or  increases  their 
tension  (pressure)  decreases  likewise  the  danger  of  their 
ignition;  but  when  the  pressure  is  thus  increased  and  the 
gas  ignited,  the  explosion  is  more  powerful.  It  may  be 
stated  further,  however,  that,  when  an  explosion  has  once 
started,  the  force  of  the  explosion  and  the  temperature 
developed  is  greater  in  thin  seams  and  contracted  openings 
than  in  thick  seams  and  wider  openings,  owing  to  the  con- 
tracted openings  affording  less  opportunity  for  the  expansion 
of  the  gases  and  the  consequent  reduction  of  the  temperature. 

17.  The  explosive  limits  of  firedamp  under  the  varying 
conditions  of  mining  are  extremely  variable,  and  it  is  practi- 
cally impossible  to  place  any  exact  limits  within  which  mix- 
tures of  marsh  gas  and  its  associated  gases  are  explosive 
when  mixed  with  the  air  of  the  mine,  since  this  depends  on 
the  character  of  the  gases  and  the  proportions  in  which  they 
are  mixed,  as  well  as  on  the  volume  of  the  explosive  gases 
and  the  volume  and  intensity  of  the  flame  causing  the  ignition. 
Bodies  of  gas  that  are  not  explosive  under  ordinary  condi- 
tions may  suddenly  become  explosive  under  conditions  that 
are  liable  to  be  produced  at  any  moment  in  mine  workings. 

A  gaseous  condition  of  the  mine  air  that  is  considered 
safe  under  ordinary  conditions  may  be  rendered  explosive: 
(a)  by  the  suspension  of  dust  in  the  mine  air;  (b)  by  the 
increase  of  pressure  due  to  a  blast  or  to  the  explosion  of 
another  body  of  gas;  (c)  by  the  flame  of  a  blown-out  shot. 


§6  MINE  GASES  11 

18.  Afterdamp. — The  mixture  of  gaseous  products 
resulting  from  the  explosion  of  a  body  of  gas  in  a  mine  is 
called  afterdamp;  its  composition  is  extremely  variable, 
depending  on  the  conditions  of  the  explosion — whether  or 
not  they  were  favorable  to  complete  combustion.  The  char- 
acter of  the  afterdamp  is  greatly  affected  by  the  relative 
proportions  of  the  air  and  marsh  gas  (methane)  forming 
the  firedamp.  When  the  firedamp  contains  9.66  per  cent,  of 
macsh  gas,  there  is  sufficient  air  in  the  mixture  for  the  com- 
plete combustion  of  the  carbon  and  hydrogen  of  the  marsh 
gas.  When  the  firedamp  contains  a  greater  proportion  of 
gas  than  this,  there  is  insufficient  air  for  its  complete  com- 
bustion; and  when  less  gas  is  present,  there  is  an  excess 
of  air  over  what  is  needed  for  the  combustion  of  the  gas. 
The  complete  combustion  of  firedamp  in  air  produces  carbon 
dioxide  (carbonic-acid  gas),  COa,  and  water,  ff,O,  mixed 
with  the  nitrogen  of  the  air  that  remains  unchanged.  Fire- 
damp containing  an  excess  of  marsh  gas,  CHt,  or  an  insuffi- 
ciency of  air  for  its  complete  combustion,  produces  carbon 
dioxide,  CO,,  carbon  monoxide,  CO,  water,  H,O,  and  free 
hydrogen,  H;  the  proportion  of  carbon  dioxide  and  water 
produced  decreases,  and  the  proportion  of  carbon  monoxide 
and  free  hydrogen  increases,  as  the  excess  of  marsh  gas  in 
the  original  firedamp  mixture  is  increased.  Experiments  in 
the  laboratory  show  that  a  mixture  of  one  volume  of  marsh 
gas  with  four  and  one-half  volumes  of  air  produces  nine 
volumes  of  carbon  monoxide  for  one  of  carbon  dioxide,  and 
much  free  hydrogen,  together  with  a  little  water.  It  has 
been  concluded,  therefore,  that  under  favorable  conditions 
of  temperature  the  burning  of  a  firedamp  mixture  containing 
one  volume  of  gas  to  three  volumes  of  air  will  produce  only 
carbon  monoxide  and  free  hydrogen  mixed  with  the  remain- 
ing nitrogen  of  the  air;  this  forms  the  most  deadly  afterdamp. 

Afterdamp  frequently  contains  a  limited  proportion  of 
nitrous  oxide  (laughing  gas).  Both  this  gas  and  carbon 
monoxide  act  as  narcotics  to  produce  stupor  and  unconscious- 
ness. Extremely  small  percentages  of  carbon  monoxide  are 
quickly  fatal.  Victims  of  this  gas  have  been  often  found  in 


12  MINE  GASES  §C 

lifelike  positions,  and  with  a  peaceful  and  smiling  expression 
on  their  dead  faces.  In  one  instance,  a  man  was  found  with 
his  hand  to  his  mouth  in  the  act  of  biting  a  piece  of  bread; 
these  victims  show  no  bruises  or  injury  to  the  body,  but  have 
died  from  the  poisonous  effects  of  the  afterdamp. 


IGNITION  OF  GASES 

19.  Inflammable     Mine     Gases. — The     inflammable 
gases  commonly  occurring  in  mines  are  marsh  gas  (methane, 
or    carbureted   hydrogen),    CHt)  carbon    monoxide    (white- 
damp),  CO,  and  hydrogen  sulphide  (sulphureted  hydrogen, 
or  stinkdamp),  H*S.     Any  of  these  gases  will  ignite  in  the 
presence  of  air  or  oxygen  when  the  temperature  of  the  gas 
is  raised  to  its  point  of  ignition.     Mines  giving  off  marsh 
gas  in  dangerous  quantities  are  called  gaseous,  or  fiery, 
mines,  and  the  working  of  such  mines  is  often  extremely 
difficult  owing  to  the  danger  of  igniting  the  gas  and  causing 
an  explosion  more  or  less  disastrous  in  its  results. 

20.  Temperature  of  Ignition. — Each  of  the  inflam- 
mable gases  requires  for  its  ignition  a  certain  definite  tem- 
perature, known  as  the  temperature  of  ignition  of  the  gas. 
After  ignition  has  taken  place  and  flame  is  produced,  if  the 
burning  gas  is  cooled  by  contact  with  a  cold  surface  below 
the  temperature  of  ignition,  the  flame  is  extinguished.     The 
temperature  of  ignition  of  the  common  mine  gases  is  given, 
approximately,  in  Table  III. 

TABLE  III 


Gases 

Temperature 
of  Ignition 
Degrees  F. 

Marsh  gas  (methane,  carbureted  hydrogen),  CHt 
Ordinary  illuminating  gas    ...        ...        .    . 

1,202 
1,198 

Carbon-monoxide    CO 

I   2O2 

Hydrogen,  H              

I,  O8O 

Hydrogen  sulphide   ff*S 

7^O 

§6  MINE  GASES  13 

21.  Temperature  of  the  Flame. — The  temperature  of 
the  flame  of  a  burning  gas  is  not  a  fixed  temperature,  as  is 
its    temperature   of   ignition.     The  combustion  of  a  given 
weight  of  a  gas  produces  a  certain  number  of  heat  units,  but 
the  temperature  of  the  combustion  will  vary  greatly  accord- 
ing  to   the  conditions   under  which   the  combustion    takes 
place.     If  flartie  is  produced,  the  temperature  of  the  flame 
will  likewise  vary  according  to  the  surrounding  conditions. 
While  the  rapidity  "of  the  combustion  tends  to  increase  the 
temperature,   the  influx  of   cold   air,   or  contact   with   cold 
surfaces,   reduces  it,   and   may  even  extinguish  the  flame. 
The  presence  of  moisture  and  its  conversion  into  steam  also 
reduces  the  temperature  of  the  resulting  products  of  com- 
bustion.    The  flame  of  an  explosion  of  marsh  gas  (methane) 
may  have  any  temperature  varying  from  1,202°  F.  to  3,902°  F. 
(assuming  gas  at  constant  volume),  the  former  being  the 
temperature  of  ignition   and  the  latter  the  greatest  initial 
temperature  developed  by  the  complete  explosion  of  this  gas. 
A   free   expansion  of  the   gases  produced  in   an   explosion 
rapidly  lowers  the  temperature  of  the  burning  gases,  while  a 
contracted  condition  of   the  mine  workings    increases  this 
temperature. 

In  blasting  with  black  powder,  the  flame  of  the  blast  may 
likewise  vary  from  1,200°  F.  to  about  3,600°  F.,  according  to 
the  conditions  under  which  the  charge  is  exploded.  Ordi- 
narily, the  flame  projected  from  the  mouth  of  a  hole  in 
blasting,  or  the  flame  of  a  blown-out  shot,  may  be  assumed 
as  having  a  temperature  of  about  2,000°  F.  A  knowledge  of 
the  temperature  of  flame  is  important  in  considering  the 
ignition  of  mine  gases,  mine  explosions,  the  safety  lamp, 
and  the  use  of  explosives  for  blasting  in  the  mine. 

22.  Causes   of    the  Ignition   of    Mine   Gases. — The 

ignition  of  an  inflammable  gas  requires  some  means  of  rais- 
ing its  temperature  to  a  point  at  least  equal  to  the  tempera- 
ture of  ignition.  The  cause  of  ignition  may  be:  the  flame 
of  a  naked  lamp,  of  a  match,  or  of  a  defective  safety  lamp; 
the  flame  incident  to  blasting;  sparking  or  incandescence  ol 

1  If,      7 


14  MINE  GASES  §6 

electric  wires;  a  mine  fire;  etc.  Each  of  these  causes  pro- 
duces a  temperature  greater  than  the  temperature  of  ignition 
of  marsh  gas  (methane),  which  cannot  be  ignited  by  a  glow- 
ing ember  or  spark  of  wood  where  no  flame  is  present. 

A  peculiarity  in  the  ignition  of  marsh  gas  is  that  the  tem- 
perature must  be  maintained  at  or  above  the  temperature  of 
ignition  of  the  gas  for  a  certain  period  of  time  before  the 
ignition  of  the  gas  will  take  place.  This  time,  although  but 
the  fraction  of  a  second,  is  of  the  utmost  importance  in 
mining,  since  it  renders  possible  the  use  of  many  detonating 
explosives  without  fear  of  the  ignition  of  the  gas.  The 
explosion  of  dynamite,  for  example,  develops  a  high  initial 
temperature  much  above  the  ignition  temperature  of  marsh 
gas,  but  so  rapid  is  the  action  of  the  explosive  that  this  high 
temperature  is  only  maintained  for  a  very  short  time.  The 
expansion  of  the  gas  that  immediately  follows  the  explosion 
lowers  the  temperature  to  a  point  considerably  below  the 
ignition  temperature  of  marsh  gas,  and  prevents  the  ignition 
of  this  gas.  This  fact  also  accounts  for  the  absence  of  any 
considerable  amount  of  flame  in  the  use  of  such  explosives. 

23.     Ignition  of  Mine  Gas  by  Incandescent  Lamps. 

The  breaking  of  an  incandescent  electric  lamp  may  or  may 
not  be  attended  by  the  ignition  of  a  surrounding  body  of 
firedamp;  much  will  depend  on  the  kind  of  lamp  used. 
Incandescent  lamps  are  of  two  general  types,  for  low  and 
high  voltage,  the  lamps  differing  chiefly  in  the  style  of  fila- 
ment used.  A  low-voltage  lamp  designed  for  large  currents 
has  generally  a  short,  thick  filament,  or  carbon,  while  a  high- 
voltage  lamp  with  a  small  current  has  a  long,  thin  filament. 
The  character  of  this  filament,  together  with  the  manner  in 
which  the  lamp  is  broken,  in  a  large  measure  determines 
whether  the  gas  will  be  ignited  or  not. 

In  the  breaking  of  a  lamp,  two  cases  may  arise:  (1)  The 
filament  may  remain  unharmed  when  the  glass  is  broken,  in 
which  case  the  ignition  of  a  surrounding  body  of  firedamp  is 
almost  certain  to  take  place,  either  by  the  contact  of  the  gas 
with  the  glowing  filament  or  by  the  sparking  that  occurs 


§6  MINE  GASES  15 

when  the  latter  burns  out  or  is  broken.  (2)  More  com- 
monly, in  mining  practice,  the  globe  and  filament  are  both 
broken  by  the  same  blow;  in  this  case,  the  question  of  the 
ignition  of  the  gas  will  depend  almost  wholly  on  the  kind  of 
filament.  The  rush  of  the  gas  and  air  into  the  vacuous  space 
at  the  instant  of  the  breaking  of  the  lamp  causes  a  momentary 
cooling  not  only  of  the  explosive  mixture  but  also  of  the 
filament.  The  thin  filament  of  a  high-voltage  lamp  is  cooled 
very  rapidly,  much  more  quickly  than  the  thick  filament  of  the 
low-voltage  lamp,  and  during  this  short  moment  of  cooling, 
the  filament  is  broken  by  the  same  blow  that  broke  the  globe. 
The  rapid  cooling  of  the  thin  filament  is  accomplished  before 
the  temperature  of  the  explosive  mixture  can  be  brought 
to  the  point  of  ignition  of  the  gas;  in  other  words,  the  thin 
filament  of  a  high-voltage  lamp  does  not  contain  sufficient 
heat  to  raise  the  temperature  of  the  explosive  mixture  rushing 
on  it  to  its  point  of  ignition.  The  thicker  filament  of  a  low- 
voltage  lamp  contains  more  heat,  and  is  not  cooled  as  rapidly 
by  the  rush  of  the  expanding  air  and  gas,  and  enough  heat 
is  retained  by  this  filament  to  cause  the  ignition  of  the  gas. 

24.  The   Condition  of  Air  in  Mines. — The  gaseous 
condition    of   mine    air   means    the    proportion    of    noxious 
gases  contained  in  the  air  circulating  through  the  mine.     A 
certain    proportion    of    such    gases    in    mine    air   produces: 
(1)   an  explosive  atmosphere;   (2)   a  dangerous  atmosphere, 
which  if  breathed  affects  the  respiration  and  may  produce 
insensibility;   (3)   a  fatal  atmosphere,  producing  death  in  a 
short  time;   (4)  an  extinctive  atmosphere,  in  which  the  flame 
of  a  candle  or  an  ordinary  oil  lamp  will  not  burn.     The 
nature  of  the  gas  present  and  the  extent  to  which  the  oxygen 
of  the  air  has  been  diminished  determine  which  of  these 
effects  is  produced. 

25.  An  explosive  condition  of  the  mine  air  is  devel- 
oped when  the  air  contains  a  certain  proportion  of  inflammable 
gas.     There  is  a  definite  proportion  of  air  and  each  of  the 
explosive  gases  that  produces  the  maximum  explosive  effect, 
but  for  each  gas  there  is  a  lower  and  a  higher  explosive  limit, 


16 


MINE  GASES 


and  any  proportion  of  gas  and  air  between  these  limits  forms 
an  explosive  mixture.  The  lower  and  higher  limits  determine 
the  explosive  range  of  the  gas.  Marsh  gas  (methane)  has  the 
least  explosive  range  of  any  of  the  inflammable  mine  gases, 
and  hydrogen  the  greatest;  the  explosive  range  of  carbon 
monoxide  (carbonic  oxide)  is  almost  equal  to  that  of  hydro- 
gen. Table  IV  gives  the  proportions  of  gas  and  air  forming 
the  lower  and  higher  explosive  limits  for  the  more  important 
mine  gases. 

TABLE  IV 


Gases 

Lower  Explosive 
Limit 

Higher  Explosive 
Limit 

Marsh  gas  (methane)  ,  CH<  . 
Ethy  lene  (  olefiant  gas  )  ,  C,H. 
Carbon  monoxide  (carbonic 
oxide),  CO    

i  :  5 
i  :  4 

i  '  ii 

i  :  13 
i  :  22 

i  ;  75 

Hydrogen,  H        .        .    . 

i  *  •» 

i  :  72 

26.  In  a  dangerous  atmosphere,  the  danger  may  arise 
from  an  explosive  condition  of  the  air  or  from  the  presence 
of  poisonous  or  other  noxious  gases.  A  fatal  atmosphere 
is  one  containing  such  a  percentage  of  these  gases  as  will 
produce  results  fatal  to  life.  A  dangerous  atmosphere  when 
breathed  for  a  long  period  of  time  may  produce  fatal  results. 
The  poisonous  mine  gases  are  carbon  monoxide,  CO,  i  per 
cent,  of  this  gas  being  fatal  to  life  when  breathed  for  some 
time,  and  hydrogen  sulphide,  HtS,  about  1  per  cent,  of  this 
gas  being  likewise  fatal  when  breathed  a  sufficient  length  of 
time.  An  atmosphere  in  which  lights  are  extinguished  is  not 
always  dangerous  to  life,  nor  will  lights  always  go  out  in  an 
atmosphere  that  is  dangerous  to  life.  Lights  are  often 
extinguished  by  an  atmosphere  that  may  be  breathed  for  a 
long  time  without  injury  further  than  a  possible  headache; 
on  the  other  hand,  lights  often  continue  to  burn  brightly  in 
an  atmosphere  that  will  cause  insensibility  and  death  in  a 
short  time. 


MINE  GASES 


17 


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18  MINE  GASES  §6 

Dangerous  or  fatal  atmospheres  depend  on  the  amount  of 
oxygen  and  the  nature  of  the  gases  present  in  the  air. 
Table  V  gives  the  composition,  by  volume,  of  the  fatal 
atmospheres  produced  by  the  mixture  of  air  with  the  several 
mine  gases  that  are  commonly  said  to  be  irrespirable. 

It  will  be  observed  that,  in  the  case  of  the  poisonous 
gases,  a  very  small  percentage  of  the  gas  added  to  the  air 
produces  a  fatal  atmosphere,  notwithstanding  that  the  per- 
centage of  oxygen  in  this  case  remains  almost  normal.  In 
the  case  of  both  nitrogen  and  marsh  gas,  the  addition  of  the 
gas  to  the  air  does  not  produce  a  fatal  effect  until  the  amount 
of  oxygen  in  the  mixture  has  been  reduced  below  what  is 
necessary  to  support  life.  The  minimum  amount  of  oxygen 
required  in  the  air  to  produce  fatal  results  varies  somewhat 
with  the  individual.  A  strong,  healthy  person  may  be 
revived  from  insensibility  after  exposure  to  an  atmosphere 
containing  a  less  percentage  of  oxygen,  while  a  weak  person 
may  succumb  to  an  atmosphere  containing  a  somewhat 
greater  percentage  than  that  given  in  the  table;  when  an 
atmosphere  containing  but  10  per  cent,  of  oxygen  has  been 
breathed  for  10  or  12  hours,  the  result  will  prove  fatal  in  the 
majority  of  cases.  It  will  be  observed,  also,  that,  although 
carbon  dioxide  (carbonic-acid  gas)  is  not  considered  one  of 
the  poisonous  mine  gases,  a  fatal  atmosphere  is  produced 
when  18  per  cent,  of  this  gas  is  present  in  the  air,  although  the 
oxygen  of  the  air  has  only  been  reduced  thereby  to  17.2  per 
cent.  This  is  due  to  the  effect  produced  by  the  carbon  dioxide 
on  the  system,  there  being  a  marked  difference  between  the 
action  of  this  gas  and  that  of  marsh  gas  or  nitrogen. 

27.  The  extinctive  character  of  an  atmosphere 
depends  chiefly  on  the  absence  of  a  sufficient  amount  of 
oxygen  to  support  combustion.  Table  VI  gives  the  com- 
position, by  volume,  of  pure  air  in  comparison  with  that  of 
several  atmospheres  in  which  the  flame  of  a  candle  or  an 
ordinary  oil  lamp  is  extinguished.  These  atmospheres  have 
been  determined  by  experiment,  and  represent  in  each  case 
the  point  where  extinction  begins. 


MINE  GASES 


19 


Each  of  the  atmospheres  mentioned  in  Table  VI  is 
respirable,  although  the  last  would  be  breathed  with  diffi- 
culty and  produce  panting.  The  air  expired  from  the  lungs 
has  practically  the  same  composition  as  the  air  left  in  a 
vessel  in  which  a  candle  has  been  allowed  to  burn  until 
extinguished  by  the  products  of  its  own  combustion.  These 
two  atmospheres  also  show  an  amount  of  oxygen  slightly 
less  than  the  percentage  of  oxygen  in  the  extinctive 
atrrfosphere  formed  when  nitrogen  is  mixed  with  air.  When 
carbon  dioxide  (carbonic-acid  gas)  is  mixed  with  air,  the 

TABLE  VI 


< 

Oxygen 

Nitrogen 

Carbon 
Dioxide, 
CO, 

Pure  Air 

70  3O 

trace 

Extinctive  Atmospheres 


Air  expired  from  the  lungs  .    . 

16.15 

79.90 

3-95 

Atmosphere    remaining    after 

candle     or    oil     flame     has 

burned  until  extinguished  .    . 

16.05 

80.80 

3-15 

Mixture  of  air  and  nitrogen 

16.38 

83.60 

Mixture    of    air    with    carbon 

dioxide  

18.06 

67.04 

14.00 

**/  'y^ 

candle  is  extinguished  when  about  2  per  cent,  more  oxygen 
is  present  than  is  the  case  with  the  other  gases  given,  prob- 
ably owing  to  the  fact  that  the  heavy  carbon  dioxide  settles 
in  the  bottom  of  the  vessel.  In  this  atmosphere.it  is  inter- 
esting to  note  that  the  percentage  of  carbon  dioxide  is  very 
much  greater  than  in  any  of  the  other  extinctive  atmos- 
pheres, showing  that  the  extinction  of  the  flame  depends 
more  largely  on  the  diminution  of  the  oxygen  than  on  the 
character  of  the  extinctive  gases — nitrogen  and  carbon 
dioxide. 


20  MINE  GASES  §6 

28.  Extinction  of  Oil  and  Gas  Flames. — There  are 
three  flames  used  for  giving  light — the  candle  flame,  the  oil 
flame,  and  the  gas  flame.     In  the  candle  flame,  three  opera- 
tions are  required:   the  melting   of   the   solid   combustible 
matter,  followed  by  the  distillation  of  the  gas,  and  the  burn- 
ing of  the  gas  to  produce  flame;  the  oil  flame  requires  but 
two  operations,  the  distillation  of  the  gas,  followed  by  the 
burning  of  the   gas;    and  the   gas  flame  requires  only  the 
burning  of  the  gas.     The  extinction  of  the  flame  in  each  of 
these  is  due  to  the  cessation  of  combustion,  owing  either 
to  the  fall  of  the  temperature  below  the  point  of  ignition  of 
the  gas,  or  to  the  lack  of  a  sufficient  quantity  of  air  (oxygen) 
to  support  the  combustion.     The  appearance  of  the  flame, 
however,  at  the  moment  of  extinction  is  quite  different  in 
the  case  of  the  candle  or  oil  flame  from  that  of  a  gas-fed 
flame.     In  a  candle  or  other  wick-fed  flame,  the  effect  of  any 
cause  impairing  the  combustion  is  to  decrease  the  distillation 
of  the  gas  and  diminish  the  size  of  the  flame.     In  the  case 
of  a  gas-fed  flame,   if   the  supply  of    gas  fed  to  the  flame 
remains  constant,  and  the  supply  of  air  or  oxygen  is  reduced, 
the  flame    enlarges   instead  of  diminishing,  in   its  effort  to 
reach  a  larger   supply  of   oxygen,  and   it  is  finally  killed  or 
dies  out  suddenly  owing  alike  to  the  inadequate  supply  of 
oxygen  and  the  reduction  of  the  temperature. 

29.  There  is  a  great  difference  in  the  effect  of  the  same 
atmosphere   on  different  flames.     This   difference    is   most 
manifest  in  the  flames  produced  by  the  burning  of  different 
gases.     The  extinctive   effect  of  any   given  atmosphere  is 
fairly   uniform    for    all    wick-fed    flames,    but    differs   with 
different  atmospheres;    thus,  13  to   16  per  cent,  of  carbon 
dioxide  (carbonic-acid  gas)  or  18  to  23  per  cent,  of  nitrogen 
is  required  to  extinguish  different  wick-fed  flames,  while  gas- 
fed  flames  require  for  their  extinction,  according  to  the  flame 
used,  from  10  to  58  per  cent,  of  carbon  dioxide,  or  17  to 
70  per  cent,  of  nitrogen,  showing  a  wide  variation  in  the 
extinction  of  gas  flames,  as  compared  with  wick-fed  flames. 
Table  VII  shows  the  composition  of  extinctive  atmospheres 


MINE  GASES 


21 


formed   by   the    mixture   of   carbon    dioxide  and   nitrogen, 
respectively,  with  air. 

Since  the  combustible  mine  gases  are  not  supporters  of 
combustion,  the  peculiar  phenomenon  is  often  manifested  in 
the  extinction  of  the  flame  of  the  lamp  when  the  latter  is 
surrounded  and  filled  with  an  atmosphere  containing  a  suf- 
ficient percentage  of  such  gas,  the  combustible  gas  itself 
burning  within  the  gauze  of  the  lamp,  the  flame  of  which 
it  Has  extinguished.  The  products  of  the  combustion  of  the 

TABLE    VII 


Air  and  Carbon 

Air  and 

Kind 

Dioxide 

\  Nitrogen 

of 

Fuel 

Flame 

O 

N 

CO, 

0 

N 

09 

Alcohol  (methyl  or  wood)   . 

18.3 

68.7 

13 

17.2 

82.8 

rt 

Alcohol  (absolute)     .... 

67.9 

16.6 

83.4 

CG 

Candle      

18.1 

67.9 

14 

16.4 

83.6 

1 

Paraffin  oil  

17.9 

67.1 

IS 

16.2 

83.8 

^) 
_o 

Colza    oil    and    petroleum 

fe: 

(equal  parts)      

17.6 

66.4 

16 

16.4 

83.6 

Cfl 

Marsh  gas  (methane)    .    .    . 

18.9 

71.1 

10 

17.4 

82.6 

i 

Carbon  monoxide  (carbonic- 

rt 

oxide  gas)    

16.0 

60.0 

24 

je.  I 

84.0 

w 

Ethylene  (olefiant  gas)     .    . 

15-5 

58.5 

m^t 
26 

*  o  •  * 

13.2 

uif  »y 

86.8 

O 

Hydrogen    

8.8 

33-2 

58 

6-3 

93-7 

gas  assist  in  the  extinction  of  the  wick-fed  flame  of  the  lamp, 
while  the  extinctive  gas  itself  continues  burning,  owing  to 
the  different  effect  of  the  same  atmosphere  on  different 
flames.  This '  principle  is  illustrated  in  the  application  of 
the  hydrogen  flame  to  the  safety  lamp.  Such  a  flame 
will  continue  to  burn  long  after  the  common  oil-fed  flame 
has  been  extinguished,  and  the  same  principle  may  have 
much  to  do  with  the  wide  propagation  of  a  flame  by  carbon 
monoxide. 


22  MINE  GASES  §6 

30.  Effect  of  Coal  Dust. — Coal  dust  suspended  in  the 
air  of  mine  workings  is  a  most  important  factor  on  account 
of  its  influence  on  flame.  Much  depends  on:  (1)  the  quan- 
tity and  fineness  of  the  dust  suspended  in  the  air;  (2)  the 
inflammability  of  the  coal;  (3)  the  presence  of  gas  in  the  air; 
(4)  the  volume  and  intensity  of  the  flame  acting  on  the  sus- 
pended dust.  In  a  dry,  dusty  atmosphere,  the  flame  of  an 
ordinary  lamp  is  lengthened.  A  flame  of  larger  volume  and 
greater  intensity,  such  as  the  flame  of  a  blast  or  the  flame  of 
an  explosion,  is  often  carried  long  distances  by  feeding  on 
the  carbon  monoxide  (carbonic  oxide)  that  is  formed  from 
the  dust  suspended  in  the  air.  All  coal  dust  is  not  equally 
inflammable,  and  the  effect  produced  on  flame  is  propor- 
tionate to  the  fineness  and  inflammability  of  the  dust  and  the 
amount  of  volatile  matter  contained  in  it.  The  dust  of 
anthracite,  for  example,  is  far  less  inflammable  than  the  dust 
of  bituminous  coal,  and  for  this  reason  a  gaseous  and  dusty 
anthracite  mine  is  not  as  dangerous  as  a  gaseous  and  dusty 
bituminous  mine.  The  dust  of  anthracite  is,  however,  not 
without  effect  on  a  flame;  and  the  fine  dust  of  any  combusti- 
ble substance,  when  suspended  in  the  air  and  acted  on  by  a 
flame,  will  increase  the  volume  of  the  flame. 


MINE  EXPLOSIONS 


TYPES    OF    EXPLOSIONS 

31.  The  term  mine  explosion  relates  to  a  more  or  less 
violent  explosive  disturbance  caused  by  the  ignition  of  gas 
or  dust  present  in   the  air  of  the  mine.     There  are  three 
general  types  of  mine  explosions:    gas  explosions,  dust  explo- 
sions, an  explosion  of  gas  and  diist  combined.     These   types 
differ  both  in  the  character  of  the  explosion  and  the  compo- 
sition of  the  afterdamp  or  gaseous  products  remaining  after 
the  explosion. 

32.  Gas  Explosion. — The  ignition  of   a  body  of  fire- 
damp is  accompanied  by  an  extremely  rapid  expansion  of  the 


§6  MINE  GASES  23 

gases,  due  to  the  high  temperature  produced  by  the  combus- 
tion. The  expansion  is  sudden  and  violent  and  occurs  with- 
out warning,  and  the  force  of  the  explosion  is  often  sufficient 
to  do  great  damage.  When  the  firedamp  mixture  consists 
of  more  or  less  pure  marsh  gas  (methane),  the  effects  of 
the  explosion  are  perhaps  more  local  than  when  the  mixture 
contains  a  considerable  amount  of  other  gases,  particularly 
carbon  monoxide,  (carbonic  oxide),  or  when  coal  dust  is 
present. 

The  effect  of  a  gas  explosion  depends  on  numerous  con- 
ditions: (1)  The  size  of  the  workings  with  relation  to  the 
body  of  gas  exploded;  the  explosion  of  a  body  of  gas  in 
contracted  mine  workings  will  produce  more  violent  effects 
than  the  explosion  of  a  similar  body  of  gas  when  the  work- 
ings are  more  spacious  and  the  free  expansion  of  the  gas  is 
unhindered.  (2)  The  kinds  and  amounts  of  gas  present  in 
the  explosive  mixture  determines  its  explosive  condition. 
(3)  The  temperature  and  velocity  of  the  air  in  circulation. 
A  low  temperature  of  the  air-current  tends  to  limit  the 
extent  of  the  explosion,  while  a  high  velocity  of  the  air- 
current  tends  to  increase  the  extent  of  the  explosion.  These 
conditions  and  many  others  connected  with  explosions  of 
mine  gases,  such  as  the  wet  or  dry  condition  of  the  work- 
ings, accumulations  of  dust,  etc.,  are  so  varied  that  it  is 
difficult  to  analyze  the  effects  of  such  an  explosion.  The 
entire  subject  of  mine  explosions  is  necessarily  more  or  less 
enshrouded  in  mystery,  for  owing  to  the  suddenness  of  their 
occurrence  and  their  generally  fatal  results,  the  most  impor- 
tant witnesses  of  the  occurrence  are  usually  killed. 

33.  Dust  Explosion. — The  term  dust  explosion  refers 
to  the  rapid  conversion  of  fine  coal  dust  suspended  in  the 
mine  air  into  gas  by  the  action  of  a  flame,  and  the  explosion 
of  the  gas  thus  produced.  A  dust  explosion  thus  embraces 
two  operations:  the  distillation  of  gas  from  the  fine  dust 
suspended  in  the  air,  or  the  rapid  formation  of  gas  from 
the  dust  by  partial  combustion,  and  the  ignition  and 
rapid  combustion  of  the  gas  produced,  accompanied  by  the 


24  MINE  GASES  §6 

expansion,  with  explosive  force,  of  the  gaseous  products  of 
the  combustion. 

The  most  important  factors  in  a  dust  explosion  are  the 
fineness  and  inflammability  of  the  dust,  and  its  free  suspen- 
sion in  the  mine  air;  also,  the  volume  and  intensity  of  the 
flame  causing  ignition.  Perhaps  no  subject  of  mining  has 
received  more  careful  attention  at  the  hands  of  experi- 
menters than  that  of  dust  explosions.  It  was  supposed 
at  one  time  that  an  explosion  of  dust  was  impossible  in 
the  absence  of  gas,  many  experimenters  claiming  that  the 
presence  of  a  small  amount  of  marsh  gas  (methane),  less 
than  what  could  be  detected  by  an  ordinary  Davy  lamp,  was 
absolutely  necessary  for  the  ignition  and  explosion  of  fine 
dust.  The  explosions  that  occurred  in  the  Camerton  col- 
lieries, Somersetshire,  England,  November,  1893,  and  that  in 
the  Timsbury  collieries  of  the  same  place,  February,  1895, 
both  of  which  were  non-gaseous  mines,  led  to  renewed 
experiments  and  discussion.  The  results  of  these  later 
experiments  confirmed  the  opinion  that  certain  inflammable 
coal  dusts  were  explosive  when  suspended  in  air  having  no 
trace  of  explosive  gas. 

A  dust  explosion  is  necessarily  not  as  sudden,  though 
fully  as  destructive  in  its  effects,  as  an  explosion  of  firedamp 
under  similar  conditions.  In  general,  the  effects  are  more 
widespread,  and,  owing  to  the  relatively  limited  supply  of 
air,  the  combustion  is  more  incomplete;  large  volumes  of 
black  smoke  containing  quantities  of  unburned  carbon  and 
coke  are  produced  and  forced  through  the  mine  passages 
and  often  projected  far  up  the  shaft  and  into  the  outer  air. 
The  afterdamp  of  a  dust  explosion  almost  invariably  con- 
tains much  carbon  monoxide,  CO,  which,  owing  to  its  wide 
explosive  range,  is  not  as  liable  to  be  extinguished  by  the 
expansion  and  cooling  of  the  gas  in  more  open  workings  as 
is  marsh  gas  (methane);  this' accounts  in  part  for  the  trans- 
mission of  the  flame  of  an  explosion  over  great  distances 
when  coal  dust  is  present. 

The  liability  of  the  flame  of  an  explosion  to  recoil  or 
return  on  its  own  path  is  greater  in  the  case  of  a  dust 


§6  MINE  GASES  25 

explosion  than  in  a  gas  explosion,  as  this  recoil  is  due  to 
carbon  monoxide  (carbonic  oxide)  left  in  the  passageways 
traversed  by  the  explosion.  The  hot  gas  collects  at  the  roof, 
and,  to  render  it  again  explosive,  it  needs  only  the  admixture 
of  fresh  air,  which  it  receives  from  the  chambers  or  rooms 
driven  off  the  passageway.  This  explosive  condition  is 
usually  found  in  the  trail  of  the  first  explosion,  and  the 
slightest  cause,  such  as  an  expansion  of  the  area  of  the 
passage,  will  cause  the  ignition  of  the  explosive  mixture 
in  the  trail,  and  the  flame  will  burn  back  along  the  roof 
of  the  passageway,  but  more  quietly  than  on  the  advance. 

34.     Combined     Gas     and     Dust     Explosion. — The 

presence  of  dust  increases  both  the  violence  and  the 
extent  of  an  explosion  of  gas,  as  there  results  in  this 
case  the  combined  effects  described  of  the  gas  and  the 
dust.  The  initial  explosion  of  the  gas  loses  none  of  its 
violence,  but  its  flame  is  extended  and  made  more  vol- 
uminous, and  projected  through  the  passageways  with  a 
more  or  less  continuous  effect,  depending  on  the  quan- 
tity, fineness,  and  inflammable  nature  of  the  dust,  and 
other  causes  previously  stated.  It  often  happens  that  an 
otherwise  local  explosion  of  a  small  body  of  firedamp 
accumulated  at  the  face  of  a  heading  is  transmitted  long 
distances  through  the  influence  of  accumulations  of  dust, 
causing  the  ignition  and  explosion  of  other  isolated  bodies 
of  firedamp.  Under  such  conditions,  it  is  frequently  very 
difficult,  if  not  impossible,  to  trace  the  explosion  by  its 
observed  effects  back  to  its  initial  point,  since  each  follow- 
ing explosion  sets  up  another  center  of  energy,  obliterating 
more  or  less  the  effects  produced  by  the  first  explosion,  and 
it  may  frequently  happen  that  any  one  of  the  following 
explosions  may  be  greater  in  its  effect  than  the  first  or 
initial  explosion,  and  may  advance  on  the  trail  of  the  first 
explosion.  It  may  be  practically  impossible  to  determine 
the  first  cause  except  by  the  evidence  of  the  survivors, 
which,  however,  is  always  more  or  less  conflicting  owing  to 
the  terror  and  excitement  of  the  situation. 


26  MINE  GASES  §6 

PHENOMENA    OF    EXPLOSIONS 

35.  The  character  of  a  mine  explosion  depends  entirely 
on  the  conditions  with  respect  to  the  explosive  mixture  of 
gases,  size  and  condition  of  the  workings,  quantity  of  air  in 
circulation,  etc.     No  two  explosions  under  seemingly  like 
conditions  present  the  some  phenomena,  and  it  often  hap- 
pens that,  owing  to  the  multitudinous  conditions  attending 
explosions,  the  results  are  widely  different.      The  following 
are,  however,  a  few  general  phenomena   that   apply  to  all 
explosions. 

36.  The  force  developed  by  the  explosion  of  a  body  of 
gas  is  evidenced   by  the   destruction   it   accomplishes,  and 
depends  on  the  quantity   and  composition  of  the  explosive 
mixture.     The  immediate  destructive  effect  of  the  explosion 
is   inversely  proportional    to  the  size  of   the  workings;  for 
example,  the  explosion  of  a  small  body  of  gas  in  a  thin  seam 
with  contracted  openings  will  prove  equally  destructive  with 
that  of  a  much  larger  body  of  gas  in  a  thick  seam  with  wider 
and  more  extended  openings.      The  center  of  an  explosion  is 
generally  made  known  by  the  evidences  of  explosive  force 
radiating    from   a  common   point.     The   direction   in  which 
loose  material,  as  coal,  timbers,  cars,  and  even  doors  and 
brattices,  have  been  blown,  indicates  the  direction  of  the 
force  and  locates  the  center  of  the  explosion.     Each  local 
explosion  due  to  the  ignition  of  a  separate  body  of  firedamp 
forms  the  center  of  an  explosive  force  representing  more 
or  less  closely  the  quantity  and  explosiveness  of  the  gas 
accumulated  at  that  point. 

37.  An  important  phenomenon  attending  nearly  all  mine 
explosions  is  the  transmission  of  the  flame  of  the  initial 
explosion  to  other  parts  of  the  mine,  igniting  other  bodies 
of  gas,  and  propagating  throughout  the  mine  what  would 
otherwise  have  been  a  local  explosion.     The  manner  and  the 
distance  the  flame  of  an  explosion  is  transmitted  will  depend 
on  the  amount  and  composition  of  the  explosive  mixture  and 
on  numerous  conditions  with  respect  to  the  air-current  and 


§6  MINE  GASES  27 

the  mine  entries  and  workings.  The  flame  may  advance  at  a 
moderate  velocity,  quietly  sweeping  the  roof  of  the  passage, 
or  as  a  wild  rush  of  fire  filling  the  entire  entry  with  flame, 
dust,  and  debris,  propelled  at  a  high  velocity  by  the  explo- 
sive energy.  The  path  traversed  by  the  flame  is  frequently 
a  haulage  road  in  preference  to  other  passageways,  which 
may  be  explained  by  the  fact  that  the  powdered  coal  and 
dust  of  the  haulage  road  feed  the  flame  of  the  explosion. 
On,the  other  hand,  an  explosion  may  pass  by  a  dry,  dusty 
heading  and  advance  for  a  long  distance  over  a  wet  haulage 
road,  for  the  reason,  probably,  that  the  supply  of  fresh  air 
needed  to  propagate  the  explosion,  as  well  as  a  larger  quan- 
tity of  fine  coal,  is  found  along  the  haulage  road.  In  general, 
it  may  be  said  that  the  question  of  air  supply  determines 
very  largely  the  course  of  the  explosion,  since  the  oxygen  of 
the  air  is  necessary  for  the  combustion  that  takes  place. 

In  a  dusty  mine,  where  the  flame  has  been  propagated  long 
distances  by  the  dust  of  the  roadways,  or  where  the  flame 
of  a  second  explosion  travels  back  on  the  trail  of  the  initial 
explosion,  it  is  often  difficult,  if  not  impossible,  to  determine 
the  starting  point  and  to  ascertain  with  certainty  the  first 
cause,  so  as  to  fix  the  responsibility  for  the  occurrence. 

38.  The  advance  of  a  mine  explosion  is  almost 
invariably  greatest  in  a  direction  against  the  air-current. 
The  distance  the  flame  of  an  explosion  will  advance  in  the 
opposite  direction,  or  with  the  air,  is  dependent  on  the  size 
of  the  entries,  the  quantity  of  air  in  circulation,  and  the 
amount  of  fresh  air  that  can  reach  the  entry  on  the  return 
side  of  the  explosion;  on  this  side,  the  flame  dies  out  sooner 
or  later  for  lack  of  air  to  support  the  combustion.  On  the 
other  hand,  there  is  always  a  plentiful  supply  of  air  to  sup- 
port the  combustion  on  the  intake  side  of  the  explosion, 
and  for  this  reason  the  flame  advances  more  rapidly  and 
further  against  the  air-current. 

The  distance  traveled,  the  rapidity  of  the  advance,  and  the 
violence  of  the  explosion  depend  on  the  initial  explosive 
force,  the  quantity  of  air  in  circulation,  its  gaseous  condition 


28  MINE  GASES  §6 

and  temperature,  and  the  condition  of  the  entry  as  being  dry 
or  wet,  and  as  containing  a  greater  or  less  quantity  of  dust, 
and  the  inflammability  and  fineness  of  the  dust;  also,  the  size 
of  the  passageway  traversed,  and  the  area  of  standing  work- 
ings connecting  with  or  opened  off  from  the  entry. 

39.  The  arrest  of  an  explosion  may  be  due  to  numer- 
ous causes.     On  the  return  side  of  the  explosion,  the  flame 
is  checked  and  finally  arrested  usually  from  an  insufficient 
supply  of  air.     On  the  intake  side  of  the  explosion,  the  flame 
is  usually  arrested  by  a  reduction  of  temperature  from  con- 
tact with  the  cold  air-current,  or  by  a  sudden  expansion  of 
the  burning  gas  due  to  an  enlargement  of  the  sectional  area 
of  the  passageway  or  the  proximity  of  adjoining  workings. 
At  times,  the  advance  of  the  flame  is  so  sudden,  owing  to 
the  initial  force  of  the  explosion,  as  to  cause  a  too  rapid 
expansion  and  a  consequent  reduction  of  the  temperature, 
and  the  flame  is  extinguished  from  no  other  apparent  cause. 
A  sufficient  quantity  of  carbon  dioxide  (carbonic-acid  gas) 
or  blackdamp  might  cause  the  extinction  of  the  flame.    Only 
10  per  cent,  of  this  gas  is  necessary  for  the  extinction  of  the 
flame  of  pure  marsh  gas  (methane)  and  24  per  cent,  for  the 
extinction  of  the  flame  of  carbon  monoxide  (carbonic  oxide). 
Where  a  certain   percentage  of   ethylene  (olefiant  gas)    is 
mixed  with  the  marsh  gas,   a  larger  percentage  of  carbon 
dioxide  would  be  required  for  the  extinction  of  the  flame. 
The   spraying  or  wetting  of  the  roof,  sides,  and  floor  of  a 
dusty  passageway,  while   reducing  the  quantity  of  fine  dust 
ordinarily  suspended  in  the  air,  does  not  have  the  effect  of 
materially  arresting  the  advance  of  the  flame  of  an  explo- 
sion.    This  can  only  be  accomplished  by  the  presence  of  a 
much  larger  quantity  of  water  than  it  is  possible  to  intro- 
duce by  spraying.    In  many  cases,  the  flame  of  an  explosion 
has  traversed  200  yards  of  entry  where  the  roof,  sides,  and 
floor  were  in  a  very  wet  condition. 

40.  The  recoil  of  an  explosion  is  the  return  of  the 
flame  on  its  own  path.     Fig.  1   represents  a  portion  of  a 
mine  and  the  manner  in  which  the  flame  of  an  explosion 


§6  MINE  GASES  29 

advancing  against  the  air  may  be  arrested  and  the  recoil 
take  place.  In  the  figure,  the  flame  of  the  burning  gases 
has  advanced  along  the  intake  against  the  air-current  to  a 
point  where  the  entry  widens  to  provide  a  double  track  or 
parting.  At  this  point,  the  volume  of  the  flame  is  expanded 


Fio.l 

and  its  temperature  reduced,  extinguishing  the  flame  on  the 
side  toward  the  air  and  arresting  its  further  advance,  and 
permitting  the  access  of  the  fresh  air  to  the  trail  of  hot  com- 
bustible gas  behind;  the  flame  then  starts  to  burn  back  on 
this  trail,  obtaining  a  sufficient  supply  of  air  for  this  purpose 
from  the  adjoining  rooms  or  chambers. 

145—8 


30  MINE  GASES  §6 


ENTERING    A    MINE    AFTER    EXPLOSIONS 

41.  Rescue    "Work. — The    work  of    rescuing  any  who 
have  been  injured  or  shut  in  a  mine  by  an  explosion  must 
be  undertaken  promptly  and  prosecuted  with  the  utmost  dili- 
gence; only  experienced  men   should  be  employed  for  this 
purpose.     Immediately  after  the  occurrence  of  an  explosion, 
messengers  should  be  despatched  for  medical   aid,   and  a 
call  made  for  volunteers  to  enter  the  mine;  the  ventilating 
apparatus  should  be  examined  to  ascertain  that  it  is  still  in 
working  order.     The  best  and  most  experienced  men  are 
selected  from  the  volunteers,  and  these  men  are  provided, 
with  safety  lamps  that  are  in  good  condition.     The  neces- 
sary materials  for  repair  work,  such  as  brattice  boards,  can- 
vas, timber,  nails,  hammers,  saws,  and  axes  are  carried  to 
the  entrance  of  the  mine.     The  mine  must  be  entered  on  the 
intake,  and  care  taken  not  to  proceed  in  advance  of  the  air. 
The  party  is  divided  into  two  divisions,  one  for  exploring 
the  air-courses  in  advance,  the  other,  and  larger  division,  for 
making  the  necessary  repairs  to  brattices,  doors,  stoppings, 
and  air  bridges  that  have  been  destroyed  by  the  explosion. 
Only  such  repairs  as  are  necessary  to  maintain  the  air-current 
ahead  of  the  exploring  party  are  made.     The  following  sug- 
gestions are  good: 

(a)  Talk  little,  and  give  no  advice  that  is  not  asked. 

(b)  Keep  a  watchful  eye  on  the  light  of  your  lamp,  and 
halt  the  moment  the  flame  becomes  unusually  dull  or  bright, 
or  is  elongated. 

(c)  Make  no   advance  ahead  of  the  air,  and  retreat  on 
feeling  the  first  symptoms  of  weakness  or  relaxation  of  the 
muscles. 

(d)  Any  survivors  should  be  carried  at  once  to  the  sur- 
face, or  to  a  point  where  fresh  air  is  traveling  and  where 
they  can  receive  medical  aid. 

42.  Care  must  be  taken  in  the  removal  of  the  injured; 
and,  as  far  as  possible,  rough  handling  should  be  avoided. 
The  treatment  of  the  patient  will  depend  on  the  character  of 


§6  MINE  GASES  31 

the  injury;  when  possible,  lay  the  patient  on  his  back  with 
head  and  shoulders  slightly  raised.  If  he  is  unconscious, 
loosen  all  collars,  waistbands,  and  belts,  and  dash  cold  water 
on  the  face;  rub  the  body  and  limbs  briskly  to  start  the 
circulation.  If  this  fails  to  revive  consciousness  and  medical 
aid  has  not  arrived,  an  effort  should  be  made  to  restore 
breathing  by  artificial  means,  as  follows:  The  tongue  should 
be  drawn  forwards,  in  the  mouth  to  prevent  the  obstruction 
of  the  throat.  The  patient  lying  on  his  back,  the  operator 
kneels  at  his  head  and  reaching  forwards  grasps  the  arms 
near  the  elbows  and  carries  them  up  in  an  extended  position. 
This  movement  allows  air  to  enter  the  lungs.  The  arms  are 
held  in  this  position  for  2  seconds,  and  then  carried  down- 
wards and  pressed  firmly  against  the  sides,  forcing  the  air 
from  the  lungs.  This  movement  is  repeated,  at  the  rate  of, 
say  15  times  per  minute  until  natural  breathing  returns.  The 
fumes  of  ammonia  or  smelling  salts  are  also  beneficial.  No 
attempt  should  be  made  to  give  stimulants  to  an  unconscious 
person  through  the  mouth,  as  there  is  danger  of  strangulation. 
Where  bleeding  results  from  the  injury,  means  should  be 
taken  to  stop  the  flow  of  blood,  especially  if  from  the 
arteries,  which  would  be  indicated  by  the  bright  red  color  of 
the  blood,  the  venous  blood  being  dark.  Profuse  bleeding 
is  checked  by  binding  a  chord,  rope,  or  bandage  tightly 
around  the  bleeding  member  above  the  wound,  or  between 
the  wound  and  the  heart.  A  knot  previously  tied  in  the 
bandage  or  rope  and  placed  so  as  to  press  more  tightly 
against  the  artery  stops  the  flow  of  blood  more  quickly.  A 
short  stick  is  often  inserted  in  the  bandage,  and  the  latter 
tightened  by  turning  the  stick. 

43.     Rescue    Appliances    and    Mine    Supplies. — At 

every  mine,  there  should  always  be  maintained  a  plentiful 
supply  of  materials  that  may  be  needed  in  case  of  emer- 
gency, such  as  props,  caps  and  timbers  of  the  sizes  used, 
oak  tracking,  iron  rails,  iron  pipes,  ties,  brattice  cloth, 
boards,  nails,  and  spikes,  together  with  a  sufficient  number  of 
extra  lamps  and  tools.  In  some  states,  the  mine  laws  specify 


MINE  GASES 


that  certain  emergency  supplies  shall  be  kept  at  the  mine; 
for  instance,  the  bituminous  mining  law  of  Pennsylvania 
requires  that  there  shall  be  constantly  on  hand  at  the  mine 
a  full  supply  of  all  materials  required  to  preserve  the  health 
and  safety  of  the  employes,  including  a  stretcher  properly 
constructed,  and  a  woolen  and  a  waterproof  blanket  in  good 
condition  for  use;  when  more  than  200  persons  are  employed, 
two  stretchers,  two  woolen,  and  two  waterproof  blankets  are 

required.  In  mines  gen- 
erating firedamp,  there  is 
required  also  a  sufficient 
quantity  of  linseed  or  olive 
oil,  splints,  bandages,  and 
linens  for  use  in  case  of 
accident. 

44.  For  entering  mine 
workings  after  an  explo- 
sion and  before  the  circu- 
lation has  been  restored, 
various  appliances  have 
been  used  by  which  a  suf- 
ficient amount  of  air  or 
oxygen  is  supplied  to  sus- 
tain life  for  a  short  time. 
In  some  of  these  appli- 
ances, the  air  is  supplied 
through  a  pipe  or  small 
tube,  and  inhaled  by  placing 
the  end  of  the  tube  in  the  mouth.  By  this  means,  a  person 
has  been  enabled  to  advance  50  yards  ahead  of  the  air.  A 
more  common  form  of  apparatus  consists  of  a  helmet,  or 
head-protector,  fitting  over  the  head  and  resting  on  the 
shoulders.  This  helmet  is  made  of  a  double  thickness  of 
leather  and  horsehide  chemically  treated  to  render  it  fire- 
proof and  waterproof. 

Fig.  2  shows  the  Vajen-Bader  helmet,  which  is  made  in 
two  sizes,  the  larger  size  being  capable  of  supplying  fresh 


FIG.  2 


§6  MINE  GASES  33 

air  for  several  hours.  The  helmet  is  about  the  same  weight 
as  that  of  a  thick  overcoat,  and  is  held  in  place  by  two  straps 
passing  under  the  arms.  An  air  cylinder  containing  air, 
at  150  pounds  pressure  per  square  inch  when  fully  charged, 
is  attached  to  the  back  of  the  helmet;  a  small  tube  conducts 
the  air  from  this  cylinder  to  a  point  within  the  helmet  close 
to  the  nostrils.  The  fresh  air  thus  forced  into  the  helmet 
creates  a  slight  downward  pressure  that  drives  the  foul  air 
thrpugh  a  collar  of  absorbent  lamb's  wool,  and  out  at  the 
bottom  of  the  helmet.  The  helmet  is  supplied  with  two  out- 
looks or  windows,  made  of  double  plates  of  clear  mica  pro- 
tected on  the  outside  by  cross-wires.  There  are  also  ear 
pieces  having  special  sounding  diaphragms  that  render  the 
hearing  distinct.  A  whistle  is  attached  in  front  to  provide  a 
means  of  signaling.  When  suitable  apparatus  is  not  at 
hand,  a  dash  may  often  be  made  into  an  impure  atmosphere 
for  the  recovery  of  a  person  overcome  by  gas,  if  a  wet 
cloth  or  a  sponge  saturated  with  vinegar  is  tied  over  the 
mouth  and  nose.  This  affords  a  temporary  protection  from 
the  inhalation  of  the  noxious  gas. 


PREVENTION  OF  EXPLOSIONS 

45.     Reducing   the    Liability    to    Explosion. — The 

liability  to  explosion  may  be  reduced  by  removing,  as  far 
as  possible,  those  causes  and  conditions  that  lead  to  them. 
Briefly  stated,  the  causes  of  mine  explosions  are:  the  ignition 
of  a  body  of  firedamp  by  any  means;  or  the  raising  and  firing 
of  an  atmosphere  of  dust  by  the  flame  of  a  blast  or  a  blown- 
out  shot;  or  the  successive  quick  firing  of  two  or  more  shots 
in  a  close  place.  To  remove  these  causes  and  lessen  the 
liability  of  the  occurrence  of  a  mine  explosion,  the  following 
precautions  should  be  adopted:  (1)  The  ventilating  current 
should  be  sufficient  to  dilute,  render  harmless,  and  sweep 
away  the  gases  produced  in  the  mine.  (2)  The  air  should 
be  distributed  to  the  several  districts  of  the  mine  in  such 
quantities  that  the  velocity  of  the  current  will  not  exceed  450 
feet  per  minute  in  any  place  where  safety  lamps  are  used. 


34  MINE  GASES  §6 

(3)  The  velocity  of  the  air-current  at  the  face  should  not  be 
less  than  4  or  5  feet  per  second,  and  should  be  sufficient  to 
sweep  away  the  gases  that  would  otherwise  accumulate  in 
the  cavities  of  the  roof  or  other  places  in  the  workings;  when 
necessary,  special  brattices  should  be  erected  to  deflect  the 
air-current  so  as  to  sweep  the  places  where  gas  is  liable  to 
collect.  (4)  A  careful  and  regular  examination  should  be 
made  of  all  gaseous  workings  by  a  competent  fire  boss 
before  the  time  of  commencing  each  shift,  and  due  precau- 
tions should  be  taken  to  prevent  men  from  entering  places 
where  gas  has  been  found.  (5)  The  use  of  naked  lights 
should  not  be  permitted  in  a  gaseous  mine.  (6)  All  safety 
lamps  should  be  carefully  cleaned,  examined  or  tested,  and 
securely  locked  before  being  taken  into  the  mine.  (7)  Where 
blasting  is  performed,  and  it  is  practicable  to  do  so,  the  shots 
should  be  inspected  and  fired  by  experienced  shot  firers  after 
the  men  have  left  the  mine.  (8)  Dust  or  fine  coal  should 
not  be  allowed  to  accumulate  in  the  working  places  or 
on  the  haulage  roads.  When  the  coal  is  very  inflammable 
and  the  mines  dry  and  dusty,  some  uniform  system  of  spraying 
should  be  adopted,  both  at  the  face  and  on  the  haulage  roads 
throughout  the  mine.  Too  much  reliance  should  not,  however, 
be  placed  on  the  spraying  of  the  coal.  According  to  the  con- 
clusions reached  by  the  Prussian  Firedamp  Commission,  the 
ignition  and  explosion  of  coal  dust  is  prevented  by  this  means 
only  when  50  per  cent,  of  its  weight  of  water  is  present — a 
much  larger  quantity  than  can  be  introduced  by  any  system 
of  spraying,  however  efficient. 


§6  MINE  GASES  35 


TESTING  FOR  GASES  IN  MINES 


SAFETY  LAMPS 

46.  The  miner's  safety  lamp  is  a  lamp  in  which  the 
flame  is  isolated  from  the  outside  air  by  means  of  a  wire 
gauze  chimney,  or  a  glass  chimney  and  gauze  combined.    The 
openings  in  the  lamp  for  the  ingress  and  egress  of  air  are  all 
protected  by  wire  gauze  in  such  a  manner  as  to  prevent  the 
passage  of  the  flame  of  the  lamp  through  the  gauze  under 
ordinary  conditions. 

47.  The  Principle  of  the  Safety  Lamp. — The  essen- 
tial principle  of  all  safety  lamps  consists  in  the  cooling  effect 
that  a  metal  surface  exerts  on  a  flame  with  which  it  comes  in 
contact.     The  cool  metal  lowers  the  temperature  of  the  burn- 
ing gas  in  immediate  contact  with  it,  to  a  point  below  the 
temperature  of  ignition  of  the  gas  supporting  the  flame,  and 
the  latter  is  thereby  extinguished.     This  cooling  effect  is 
observed  whenever  any  cold  surface  of  metal  is  exposed  to 
a  flame,  a  deposit  of  soot  being  formed  on  the  surface  of  the 
metal,  as  evidence  of  the  incomplete  combustion  produced 
at  that  point  by  the  cooling.     The  result  of  this  cooling  is 
the  extinction  of  the  flame. 

This  principle  was  first  applied  to  the  construction  of  the 
safety  lamp  by  Sir  Humphrey  Davy  in  1815,  who  devised  at 
that  time  what  has  since  been  known  as  the  Davy  safety 
lamp.  Davy  surrounded  the  flame  of  the  lamp  with  an  iron 
wire  gauze  in  the  form  of  a  cylinder  closed  at  the  top.  His 
experiments  showed  that  the  gauze  best  adapted  to  this  pur- 
pose was  one  composed  of  twenty-eight  parallel  wires 
(No.  28  Birmingham  wire  gauge)  to  the  inch,  forming  a 
mesh  of  784  openings  per  square  inch,  which  is  the  standard 
wire  gauze  used  in  all  safety  lamps  today. 


36  MINE  GASES  §6 

The  gauze  permits  the  free  passage  of  the  air  and  gas  into 
and  out  of  the  lamp.  The  mesh  of  the  gauze  divides  the 
passing  air  or  gas  into  fine  streamlets,  which  insures  its 
direct  contact  with  the  cool  surface  of  the  metal.  When  the 
lighted  lamp  is  placed  in  a  mixture  of  air  and  gas,  the  gas 
enters  with  the  air  and  burns  within  the  lamp,  the  products 
of  the  combustion  passing  out  through  the  upper  part  of  the 
gauze.  When  sufficient  gas  is  present,  it  sometimes  happens 
that  the  entire  lamp  fills  with  flame,  which  is  only  prevented 
from  passing  outside  the  lamp  by  the  cooling  effect  of  the 
gauze,  the  streamlets  of  burning  gas  being  cooled  and 
extinguished  in  their  attempt  to  pass  through  the  mesh  of 
the  gauze.  This  condition  is  known  as  the  flaming  of 
the  lamp. 

Under  certain  conditions,  the  flame  may  pass  through  the 
gauze  and  ignite  the  gas  outside  of  the  lamp.  When  a  lamp 
is  exposed  for  some  time  to  an  atmosphere  containing  a 
considerable  percentage  of  gas,  the  lamp  and  the  gauze  sur- 
rounding the  flame  become  heated.  This  soon  destroys  the 
protection  afforded  by  the  lamp,  as  the  passage  of  the  flame 
through  a  hot  gauze  will  occur  sooner  or  later,  according  to 
the  condition  of  the  gauze  and  the  velocity  of  the  air  passing 
the  lamp.  When  the  flame  of  the  lamp  is  allowed  to  smoke 
owing  to  its  being  too  high,  or  to  the  poor  trimming  of  the 
wick,  or  to  the  burning  of  an  inferior  oil,  the  gauze  becomes 
covered  with  a  deposit  of  soot,  and  in  this  condition  will  pass 
the  flame  more  readily.  The  fine  dust  floating  in  the  mine 
air  and  collecting  on  the  gauze  of  the  lamp  has  the  same 
effect.  A  gauze  is  also  rendered  unsafe  by  the  slightest 
defect,  which  may  be  so  small  as  to  easily  pass  unnoticed. 
For  this  reason,  lamps  are  frequently  tested,  as  well  as 
examined,  before  being  carried  into  a  mine. 


TYPES    OF    SAFETY    LAMPS 

48.  There  are  many  kinds  of  safety  lamps,  all  of  which 
embody  the  same  essential  principles  relating  to  the  isolation 
of  the  flame  of  the  lamp  from  the  outside  air.  Only  such 


§6  MINE  GASES  37 

lamps  will  be  described  as  present  distinct  and  important 
features.  As  far  as  possible,  these  features  will  be  described 
in  the  order  of  their  development,  and  the  lamps  classified 
according  to  their  use  in  the  mine. 

Lamps  may  be  divided  into  two  general  classes:  (a)  lamps 
for  testing  for  gas;  (b)  lamps  for  general  mining  use.  These 
types  differ  essentially  in  their  requirements  and  construction. 
In  general,  a  lamp  designed  for  the  purpose  of  testing  for 
gas,  does  not  make  a  good  lamp  for  general  work,  and  a  lamp 
adapted  to  general  work  is  not  and  should  not  be  as  sensitive 
to  gas  as  one  required  to  make  an  accurate  test.  A  few 
lamps,  however,  are  designed,  as  far  as  possible,  to  meet  both 
of  these  requirements. 

49.  Lamps  for  Testing  for   Gas. — The   chief  points 
considered    in    choosing    a    lamp    for    testing    for    gas   are: 
(1)   free  entry  of  air  at  a  point  below  the  flame;   (2)  a  sliding 
glass  or  metal  shield  to  protect  the  flame  from  strong  cur- 
rents;  (3)  no  reflecting  surfaces  behind  the  flame;   (4)  a  scale 
for  measuring  the  height  of  the  flame  cap  produced. 

50.  Lamps  for  General  Use. — The  points  mainly  con- 
sidered in  choosing  a  lamp  for  general  use  are:   (1)  maximum 
illuminating  power;   (2)   safety  in  strong  currents;   (3)  mini- 
mum  liability  to  accident;    (4)   diffusion  of  light  upwards; 
(5)   simplicity  of  construction  and  security  of  lock  fasten- 
ings;    (6)   appliance    for   relighting    the    lamp  when  extin- 
guished without  opening  the  lamp. 

51.  Davy  Lamp. — Fig.  3  (a)  shows  a  perspective  and 
Fig.  3  (b)  a  sectional  view  of  the  common  unbonneted  Davy 
lamp.     The    lamp    consists    of    a    solid-brass  oil  vessel,  to 
which  is  secured,  by  three  upright  standards,  a  gauze  cylin- 
der surmounted  by  a  gauze  cap,  giving  double  protection 
against  the  transmission  of  the  flame  at  the  top  of  the  cylin- 
der, where  there  is  greater  liability  of  the  gauze  becoming 
heated  or  being  burned   through.     The    gauze  cylinder  is 
generally  li  inches  m  diameter,  and,  with  its  cap,  varies 
from  4  to  6  inches  in  height,  in  different  lamps.     Iron  wire 
is  commonly  used  in  making  the  gauze,  although  copper 


38 


MINE  GASES 


wire  is  sometimes  employed,  because  it  does  not  rust  as 
quickly  as  iron.  The  oil  vessel,  standards,  and  top  of  the 
lamp  may  be  made  of  aluminum,  to  reduce  the  weight  of 
the  lamp.  The  air  for  combustion  enters  as  shown  by  the 
arrows  a,  a,  Fig.  3  (b} .  The  products  of  combustion  pass  out 
as  shown  by  the  arrows  b,  b. 

52.     A  form  of  this  lamp  known  as  the  fire-boss  Davy  is 
provided  with  a  small  harrow  oil  vessel  often  having  the 


shape  of  a  dice  cup,  which  is  a  convenient  form  for  handling. 
The  height  of  the  gauze  cylinder  of  this  lamp  does  not 
usually  exceed  5  inches.  A  similar  form  of  lamp,  in  which 
the  height  of  the  chimney  is  reduced  to  about  3i  or  4  inches: 
is  known  as  the  pocket  Davy,  and  when  not  in  use  is  frequently 
carried  in  the  pocket  by  the  fire  boss. 

The  Davy  lamp  is  often  provided  with  a  movable  metal 
shield  encircling  the  gauze  for  two-thirds  of  its  circumference, 


§6 


MINE  GASES 


39 


and  arranged  to  slide  upwards  when  desired.  This  shield 
protects  the  flame  of  the  lamp  against  strong  air-currents, 
and  is  important  when  testing  for  gas  in  airways  or  other 
places  where  the  air  is  moving  with  some  velocity. 

Owing  to  the  free  admission  of  air  through  the  gauze,  the 
Davy  lamp  gives  a  good  flame  cap  in  gas,  and  is  a  general 
favorite  with  fire  bosses.  The  lamp,  however,  in  its  simple 
form,  is  not  a  suitable  lamp  for  general  work,  because  of 
its  ^liability  to  flame;  its  illuminating 
power,  also,  is  less  than  that  of  many 
other  types  of  lamps.  The  unbon- 
neted  Davy  is  not  safe  when  exposed 
to  a  current  of  air  having  a  velocity 
greater  than  6  feet  per  second.  In 
the  hands  of  a  careful  and  experienced 
man,  the  presence  of  gas  in  amounts 
as  low  as  2j  per  cent.,  or  2  per  cent. 
under  particularly  favorable  conditions, 
can  be  detected  by  means  of  this  lamp. 

53.     Bonneted  Davy.  —  As  the  un- 

protected gauze  of  the  Davy  lamp  per- 

mits the  passage  of  the  flame  in  a  strong 

current  of  air,  it  was  found  necessary, 

soon  after  the  invention  of  this  lamp, 

to  enclose  the  gauze  in  a  tin  case  hav- 

ing a  glass  window  to  emit  the  light; 

this  form  of  the  lamp  was  commonly 

known  as  the  tin-can  Davy.     Later,  the 

tin  can  was  supplanted  by  a  brass  case  having  an  all-around 

glass  window  to  emit  the  light.     In  another  form,  commonly 

known  as  the  Jack  Davy,  the  tin  or  brass  case  was  replaced 

by  a  glass  cylinder  reaching  the  entire  height  of  the  gauze. 

In  some  lamps,  the   glass  cylinder  was  placed  within  the 

gauze,  and  in  others  outside  of  the  gauze.     In  still  another 

form,  a  low  glass  cylinder  surrounding  the  lower  portion  of 

the  gauze  was  made  to   slide  up   and  down,  being  held  in 

position  by  a  small  spring  or  screw.     This  form  of  bonneted 


40  MINE  GASES  §6 

Davy,  Fig.  4,  has  come  into  very  general  use  both  in  England 
and  in  America. 

The  bonneted  Davy  is  the  only  form  of  the  Davy  lamp 
used  in  England,  the  unbonneted  Davy  being  prohibited  by 
law.  The  unbonneted  Davy  and  Clanny  lamps  are  also  pro- 
hibited for  general  work  by  the  Bituminous  Mine  Law  of 
Pennsylvania,  but  mine  officials  are  permitted  to  use  these 
lamps  for  the  purpose  of  examining  the  workings  for  gas. 
The  bonnet  adds  much  to  the  security  of  both  of  these 
lamps  when  exposed  to  strong  currents.  There  are  numer- 
ous forms  of  bonneted  Davy  lamps  in  addition  to  those 
already  mentioned,  many  of  them  combining  features  of 
other  lamps.  Various  forms  of  deputy  or  gas-tryer's  lamps 
consist  in  some  simple  modification  of  the  Davy  lamp.  In 
many  cases,  these  features  are  not  of  sufficient  importance 
to  warrant  the  designation  of  the  lamp  by  another  name. 

54.  The  favorite  lamp  for  testing  for  gas  has  always 
been  the  common  Davy  lamp,  which  is  most  sensitive  to  gas 
owing  to  the  unobstructed  passage  of  the  air  in  and  out  of 
the  lamp.  Ordinary  sperm  or  lard  oil  is  used  in  this  lamp, 
and  the  test  for  gas  is  made  either  with  a  small  flame  or 
with  the  normal  flame.  The  flame  cap  indicating  the  pres- 
ence of  gas  is  non-luminous  and  difficult  to  be  observed 
when  there  is  less  than  2  or  2£  per  cent,  of  gas  present. 
The  more  the  flame  is  reduced  in  size  the  more  readily  this 
cap  is  observed;  but  the  small  flame  is  very  apt  to  be  extin- 
guished by  the  gas,  making  the  test  for  gas  by  this  means 
extremely  delicate  for  amounts  of  gas  less  than  2i  per  cent. 
When  the  normal  flame  is  used  for  testing,  the  light  of  the 
flame  interferes  with  the  observance  of  the  flame  cap  and 
lessens  the  delicacy  of  the  test. 

Since  the  gas  cap  formed  above  the  flame  gives  great  heat 
and  but  little  light,  fine  platinum  wire  has  been  employed  to 
indicate  by  its  incandescence  the  presence  of  the  cap,  or,  in 
other  words,  to  make  visible  the  heat  of  the  cap.  By  this 
means,  the  presence  of  as  low  as  i  per  cent,  gas  is  indicated 
on  the  normal  working  flame  of  the  lamp.  Lamps  are  made 


§6  MINE  GASES  41 

that  burn  special  fluids — such  as  alcohol,  naphtha,  benzine, 
etc.,  or  hydrogen  gas — the  flames  of  which  are  more  sensi- 
tive to  gas  than  those  of  the  common  safety-lamp  oils.  By 
the  use  of  these  lamps,  gas  may  be  detected  in  amounts 
varying  from  i  to  2  per  cent. 

55.  The     Stephenson,     or    "Geordie,"     lamp     was 

invented  in  the  same  year  (1815)  as  the  Davy  lamp,  by 
George  Stephenson,  a  mine  blacksmith.  The  lamp  consisted 
of  a  glass  chimney  surmounted  by  a  perforated  copper  cap 
and  surrounded  by  a  perforated  copper  shield.  Owing  to  the 
numerous  perforations  in  the  metal  shield  forming  the  chim- 
ney of  this  lamp,  its  principle  has  been,  to  a  certain  extent, 
confounded  with  the  principle  of  the  Davy  lamp.  The  two, 
however,  are  distinct:  in  the  Davy  lamp,  the  extinction  of  the 
flame  is  accomplished  by  its  contact  with  the  cool  metal  of 
the  gauze;  while  in  the  Stephenson  lamp,  the  flame  is  extin- 
guished, before  it  can  pass  outside  the  chimney,  by  restricting 
the  circulation  of  the  air  in  the  lamp,  thus  confining  the  prod- 
ucts of  the  combustion  within  the  lamp.  The  Stephenson 
principle,  though  unrecognized,  is  operating  in  many  of  the 
types  of  safety  lamps  at  the  present  day,  being  often  effective 
in  extinguishing  the  flame  of  the  lamp  in  gas.  "In  most  bon- 
neted lamps,  the  burned  air  in  the  upper  portion  of  the 
chimney  adds  greatly  to  the  protection  afforded  by  the  lamp. 

56.  The  Clanny  lamp  was  designed  by  Doctor  Clanny, 
to  secure  greater  protection  for  the  flame  and  at  the  same 
time    a   better   light   than  is   afforded   by  the   Davy  lamp. 
Fig.  5  (a)  is  a  perspective  and  Fig.  5  (b)  a  sectional  view  of 
the  unbonneted  lamp.     A  glass  cylinder  surrounds  the  flame 
below  the  gauze,  greatly  improving  the  illuminating  power 
of  the  lamp  and  making  it  a  favorite  lamp  for  general  use. 
The  air  enters  this  lamp  through  the  lower  portion  of  the 
gauze  and  descends  to  the  flame;  there  is  of  necessity,  there- 
fore, a  conflict  of  the  descending  and  ascending  air-currents 
within  the  lamp,  creating  a  tendency  to  smoke,  dimming  the 
glass  and  obstructing  the  light,  besides  often  clogging  the 
gauze    and    increasing    the    work    of    cleaning    the    lamp. 


42 


MINE  GASES 


The  lamp  is  not  a  good  lamp  for  testing,  as  the  conflicting 
air-currents  interfere  with  and  prevent  the  formation  of  the 
flame  cap.  The  unbonneted  Clanny  is  not  safe  when  exposed 
to  a  current  having  a  velocity  greater  than  8  feet  per  second. 

57.  The  bonneted  Clanny  is  a  good  lamp  for  general 
mining  work.  There  are  many  modifications  of  this  lamp 
constructed  to  burn  ordinary  sperm  or  lard  oil,  or  special 
fluids,  as  alcohol,  petroleum,  naphtha,  benzine,  etc.,  with  the 


purpose  of  improving  the  illuminating  power  of  the  lamp 
and  increasing  its  usefulness.  Many  essentially  Clanny 
lamps  embody  one  or  more  features  of  other  lamps;  perhaps 
the  most  important  of  these  features  is  the  deflector  arranged 
in  the  lower  portion  of  the  gauze  to  deflect  the  entering  air 
and  prevent,  to  a  large  extent,  the  conflict  of  the  air-currents 
within  the  lamp.  By  this  means,  the  tendency  of  the  lamp 
to  smoke  is  greatly  reduced  and  its  illuminating  power 


MINE  GASES 


43 


increased.  The  deflector  may  be  applied  to  many  lamps. 
Some  forms  of  the  bonneted  Clanny  have  been  tested  with- 
out failure  in  an  explosive  atmosphere  free  from  dust  and 
having  a  velocity  as  high  as  13  to  16  feet  per  second.  The 
security  of  the  lamp  under  these  conditions,  however,  will 
depend  very  much  on  the  manner  in  which  it  is  handled. 

58.  The    Howat    deflector    is    a    common    device   for 
deflecting  the  current  of  air  downwards  on  the  flame  of  the 
lamp.     It  is  shown  in  Fig.  6  attached  to  a  bonneted  lamp. 
The  device  consists  of  a  brass  shields 

midway  between  the  outer  gauze  and 
the  bonnet  and  about  1|  inches  high. 
About  i  inch  above  the  top  of  this 
shield  is  the  bottom  of  the  angle 
ring  b.  This  ring  fits  close  to  the 
gauze,  and  the  top  flange  entirely 
closes  the  space  between  the  gauze 
and  the  bonnet.  The  course  of  the 
air  to  and  from  this  lamp  is  shown 
by  the  arrows. 

59.  The  Evan  Thomas  lamp  is 

a  name  given  to  a  number  of  lamps 
that  aim  to  improve  the  illuminating 
power  and  security  of  the  Clanny 
lamp.  The  original  Evan  Thomas 
lamp  was  provided  with  a  double 
steel  bonnet  surmounting  a  double 
glass  chimney.  The  air  was  drawn  Pl°- 6 

in  at  the  top  and  descending  between  the  two  bonnets  and 
glass  chimneys  entered  the  lamp  through  protected  openings 
below  the  flame.  These  protected  openings  form  the  char- 
acteristic feature  of  an  early  type  of  lamp  known  as  the 
Eloin  lamp.  The  entering  air  passing  downwards  between 
the  double  bonnets  and  glasses  of  the  Evan  Thomas  lamp 
not  only  kept  these  cool  and  improved  the  power  of  trans- 
mission of  light  in  the  glass,  but  the  air  became  heated  and, 
entering  the  lamp  at  a  higher  temperature,  increased  the 


44 


MINE  GASES 


rapidity  of  the  combustion  and  improved  the  illuminating 
power  of  the  lamp.  Owing,  however,  to  the  liability  of  the 
inner  glass  to  be  cracked  by  the  heat  when  much  gas  was 
present,  thus  destroying  the  security  of  the  lamp,  this  form 
was  abandoned  for  a  lamp  having  a  single  glass  and  provided 
with  a  deflector  or  metal  shield  arranged  in  the  lower  part  of 
the  gauze.  This  form  of  the  lamp  is  shown  in  Fig.  7,  and 
differs  in  no  respect  from  a  bonneted  Clanny  lamp  to  which 
the  Howat  deflector  previously  described  has  been  attached. 
The  air  enters  the  lamp  by  the  small 
apertures  shown  at  a,  and  passing  up- 
wards a  short  distance  over  the  rim  of 
the  deflector  within  the  bonnet,  descends 
-to  the  flame;  the  products  of  the  com- 
bustion leave  the  lamp  through  the 
upper  part  of  the  gauze  and  the  open- 
ings b  in  the  bonnet.  The  lamp  pre- 
sents the  same  tendency  to  smoke  as 
the  Clanny  lamp;  it  is  a  good  lamp, 
however,  for  general  work,  and  may  be 
considered  safe  in  currents  having  a 
velocity  of  20  or  25  feet  per  second. 

60.  The  Mueseler  lamp  is  shown 
in  perspective  in  Fig.  8  (a)  and  in  sec- 
tion in  Fig.  8  (b) .  The  principal  fea- 
ture of  the  lamp  is  the  central  conical 
tube  or  sheet-iron  chimney  d,  which 
increases  the  draft  within  the  lamp, 
decreasing  its  tendency  to  smoke  and  improving  its  illumi- 
nating power,  besides  adding  greatly  to  the  security  of  the 
lamp  against  internal  explosions  and  reducing  the  tendency 
of  the  lamp  to  flame.  The  metal  of  the  sheet-iron  chimney, 
by  conducting  away  the  heat,  kills  the  flame  of  the  gas  burn- 
ing in  the  lamp.  The  air  enters  the  lamp  through  the  lower 
portion  of  the  gauze,  as  shown  by  the  arrows  a,  a,  and 
descends  to  the  flame  through  the  protected  openings  e,  <?;  the 
inner  tube  or  chimney  d  thus  acts  as  a  deflector  to  divide 


FIG.  7 


§6 


MINE  GASES 


45 


the  ascending  and  descending  currents.  The  unbonneted 
Mueseler  shown  in  the  figure  may  be  considered  safe  in  a 
current  having  a  velocity  of  10  feet  per  second. 

61.  The  bonneted  Mueseler  lamp  is  particularly 
adapted  to  gaseous  mines.  There  are  two  general  types  of 
this  lamp,  known  as  the  Belgian  Mueseler  and  the  English 
Mueseler,  differing  only  in  the  dimensions  of  the  gauze  and 
the  dimensions  and  position  of  the  conical  chimney.  The 


FIG.  8 

former  type  has  been  made  the  legal  lamp  for  use  in  Bel- 
gian mines.  The  inner  conical  chimney  of  the  English  Mue- 
seler is  set  higher  above  the  flame  than  in  the  Belgian  type, 
and  the  area  of  its  upper  end  much  enlarged.  The  Belgian 
Mueseler  is  generally  considered  as  being  the  safer  lamp. 
In  the  work  of  the  Royal  Commission  in  England,  these 
lamps  were  each  exposed  to  an  explosive  current  having  a 
velocity  of  48  feet  per  second.  The  Belgian  lamp  was 


46 


MINE  GASES 


simply  extinguished  after  a  few  seconds,  while  the  English 
Mueseler,  having  a  shorter  inner  tube  of  larger  sectional 
area,  caused  an  explosion  in  every  instance.  Though  a  gen- 
erally safe  lamp,  the  Mueseler  lamp  is  particularly  sensitive 
to  oblique  currents  caused  by  the  air  striking  it  at  any  angle 
other  than  a  right  angle  to  the  axis  of  the  lamp.  Attention 
was  called  to  this  fact  in  the  report  of  the  Belgian  Commis- 
sion (1873),  and  confirmed  by  the  report  of  the-  English 
Commission  (1886).  The  Mueseler  lamp,  like  the  Clanny, 
is  not  a  good  lamp  for  testing  for  gas. 


62. 


<*>  FIG.  9  <*> 

The  Marsaut  lamp  is  shown  in  Fig.  9  (a)  and  (b), 


and  like  the  Mueseler  it  is  derived  from  the  Clanny  lamp. 
Its  characteristic  feature  is  the  multiple  gauze  chimneys,  the 
object  of  which  is  to  afford  increased  protection  against 
strong  currents  of  air  and  internal  explosion.  In  the  sec- 
tional view,  Fig.  9  (b} ,  three  gauzes  are  shown;  at  times  but 
two  gauzes  are  used.  As  shown  by  the  arrows,  the  air  enter.-. 


§6  MINE  GASES  47 

the  lamp  through  the  small  openings  a,  a  under  the  bonnet 
and,  passing  through  the  lower  portion  of  the  gauze,  descends 
to  the  flame.  There  is  in  this  lamp  perhaps  an  even  greater 
tendency  to  smoke  than  in  the  Clanny  lamp,  owing  to 
the  conflicting  descending  and  ascending  currents  and  the 
increased  resistance  to  the  circulation  offered  by  the  several 
gauzes;  the  lamp  also  heats  more  quickly  in  gas  than  any  of 
the  other  forms  of  protected  lamps.  In  this  lamp,  however, 
the  /increased  confinement  of  the  gaseous  products  of  com- 
bustion in  the  upper  portion  of  the  gauze  adds  much  to  the 
security  of  the  lamp,  and  illustrates  the  principle  sought  to 
be  attained  in  the  Stephenson  lamp.  Like  the  Mueseler 
lamp,  the  unbonneted  Marsaut  may  be  considered  safe  in  a 
current  having  a  velocity  not  exceeding  10  feet  per  second. 

63.  The  bonneted  Marsaut  lamp  presents,  perhaps, 
even  greater  security  against  strong  air-currents  than  the 
bonneted  Mueseler,  and  has  been  known  to  withstand  with- 
out failure  an  explosive  current  having  a  velocity  of  50  feet 
per   second.     In  all   these    cases,   however,   much  depends 
on  the  handling  of  the  lamp  and  the  conditions  under  which 
the  test  is  made  with  respect  to  the  explosiveness  of  the  air 
and  the  presence  of  coal  dust.     The  lamp  is  not  a  good  lamp 
for  testing  for  gas.  

SPECIAL    LAMPS 

64.  Under   this   heading    such    lamps    are   included    as 
present  special  features  of  construction,  or  require  a  special 
burning  fluid,  other  than  the  oils  in  common  use.     There  are 
a  large  number  of  these  lamps,  a  comparatively  few  of  which 
have  come  into  general  use  and  will  be  described. 

65.  The    Ash worth-Hepple white-Gray    lamp    is    a 

bonneted  Clanny  lamp  combining  several  special  features  of 
construction  first  brought  out  in  the  Ashworth  and  Gray 
lamps,  respectively.  The  lamp  is  designed  for  both  testing 
and  general  use.  A  sectional  view  of  the  lamp  is  shown  in 
Fig.  10;  the  four  standards  of  the  lamp  are  hollow  tubes. 
When  the  lamp  is  used  for  testing,  the  air  enters  the  top  of 


48 


MINE  GASES 


§6 


the  standards,  as  shown  by  th»  arrows  a,  a,  and  passing  down- 
wards enters  the  combustion  chamber  through  protected 
openings  below  the  flame.  By  this  means,  a  thin  layer  of 
air  close  to  the  roof  may  be  tested 
without  tilting  the  lamp.  In  the  ordi- 
nary use  of  the  lamp,  the  lower  aper- 
tures b,  b,  in  the  standards,  which  are 
kept  closed  while  testing  for  gas,  are 
opened  to  admit  air  more  freely  to  the 
lamp.  The  flame  of  the  lamp  is  sur- 
rounded by  a  conical  glass  chimney  e, 
surmounted  by  a  small  conical  gauze  g, 
and  a  cylindrical  steel  bonnet,  termi- 
nating in  a  truncated  cone  which  re- 
duces the  area  of  its  opening  at  the 
top  and  more  effectually  controls  the 
circulation  and  prevents  downward 
currents  in  the  lamp.  This  opening  is 
protected  above  by  a  perforated  dome 
or  cap.  The  conical  shape  of  the  glass 
chimney  aids  in  the  upward  diffusion 
of  the  light,  making  easier  the  exam- 
ination of  the  roof,  while  the  same 
conical  shape  of  the  glass  chimney  and 
gauze  above  adds  to  the  security  of 
the  lamp  against  internal  explosions, 
and  assists  also  in  preventing  down- 
ward currents  in  the  lamp.  Owing  to 
the'  small  area  of  the  outlet  gauze  in  all  the  Gray  lamps,  an 
internal  explosion  is  particularly  dangerous  in  these  lamps. 
The  lamp  is  constructed  to  burn  ordinary  sperm  or  lard  oil, 
and  is  a  good  lamp  for  general  work. 

66.  The  Wolf  safety  lamp,  Fig.  11,  is  a  bonneted 
lamp  presenting  several  special  features  in  its  construction. 
The  corrugated  shield,  or  bonnet,  a  of  the  lamp  is  provided 
with  openings,  or  slots,  that  deflect  the  air-current  entering 
the  lamp  and  prevent  it  from  being  blown  directly  on  the 


FIG.  10 


§6 


MINE  GASES 


49 


gauzes.  The  lamp  has  double  gauzes,  as  shown  in  Fig.  11; 
these,  together  with  the  shield,  enable  the  lamp  to  safely 
withstand  a  9-per-cent.  gas  mixture  moving  at  a  velocity  of 
59  feet  per  second.  Naphtha  is  the  burning  fluid  used,  which 
increases  the  illuminating  power  and  renders  the  lamp  much 
more  sensitive  to  gas,  as  it  will  indicate  as  low  as  I  per  cent, 
of  marsh  gas  (methane).  Another  special  feature  of  the 
Wolf  lamp  is  its  magnetic  lock,  which  can  only  be  opened 


FIG.  11 


FIG.  12 


by  means  of  a  powerful  magnet  that  is  kept  in  the  lamp 
room.  The  self-lighting  device,  Fig.  12,  contained  in  this 
lamp  has  also  proved  of  very  great  importance,  as  lamps 
extinguished  by  an  explosion  or  otherwise  can  be  relighted, 
and  the  men  are  thus  better  able  to  escape  from  the  after- 
damp due  to  an  explosion.  The  relighting  is  accomplished 
without  opening  the  lamp,  and  can  therefore  be  done,  even 
in  the  presence  of  explosive  gases,  without  any  danger 
whatever. 


50 


MINE  GASES 


67.  The  Clowes  hydrogen  lamp,  Fig.  13  (a)  and  (i>), 
is  practically  a  Hepplewhite-Gray  lamp  with  a  somewhat  taller 
glass  chimney,  for  the  purpose  of  observing  the  flame  caps 
formed  by  the  gas  in  testing.  To  supply  a  small  hydrogen 
flame  that  is  better  adapted  to  the  purpose  of  testing  for  gas, 
a  seamless  copper  tube  c  is  inserted  in  the  oil  vessel  by  the 
side  of  the  wick  tube,  and  connected  either  below  or  at  the 
side  of  the  lamp  with  a  supply  of  compressed  hydrogen  gas 
contained  in  a  small  portable  cylinder  a,  which  is  about 
5  inches  long  and  1  inch  in  diameter,  attached  to  the  lamp, 


as  shown,  by  a  clip  b  and  a  screw  e.  When  a  test  is  to  be 
made  for  gas,  a  valve  d  is  opened  between  the  hydrogen 
cylinder  and  the  lamp,  and  the  jet  of  hydrogen  is  at  once 
ignited  by  the  oil  flame.  The  wick  is  now  pulled  down  by 
the  picker  until  the  oil  flame  is  extinguished.  The  height  of 
the  hydrogen  flame  is  then  regulated  by  the  valve  d  control- 
ling the  supply  of  this  gas,  and  the  tip  of  -  the  flame  is 
adjusted  to  the  zero  of  the  scale  in  the  lamp.  This  scale  is 
for  the  purpose  of  reading  the  percentage  of  gas,  and  con- 
sists of  a  number  of  cross-bars  supported  in  a  ladder-like 
frame  in  a  position  in  front  of  the  flame  of  the  lamp.  The 


MINE  GASES 


several  cross-bars  are  arranged  at  heights  corresponding  to 
the  heights  of  the  flame  caps  formed  by  different  percentages 
of  gas.  The  cross-bars  appear  as  dark  lines  against  the 
flame.  This  lamp  is  intended  for  the  detection  of  the  lower 
percentages  of  gas,  from  i  per  cent,  to  3  per  cent.;  when  gas  is 
present  in  larger  amounts  the  percentage  is  determined  by  the 
use  of  the  oil  flame,  i  per  cent,  with  the  hydrogen  flame 
gives  a  cap  i  inch  high,  and  2  per 
cent,  a  cap  about  li  inches  high. 

68.  The  Stokes  lamp  is  also  a 
Gray  lamp  adapted  to  the  purpose 
of  testing  for  gas  by  introducing  a 
small  alcohol  flame  at  one  side  of 
the  oil  flame.  The  lamp  is  shown  in 
section  in  Fig.  14,  having  the  small 
alcohol  lamp  a  screwed  beneath  the 
oil  vessel  of  the  lamp.  The  alcohol 
lamp  is  provided  with  a  long,  slim 
neck  or  wick  tube  b  that  extends  up 
through  the  oil  vessel  of  the  lamp. 
When  the  screw  plug  c  is  removed 
and  this  lamp  screwed  in  place,  its 
wick  is  readily  ignited  by  the  oil 
flame  at  d,  and  the  latter  may  then 
be  extinguished  by  drawing  down 
the  wick  with  the  bent  wire  picker 
that  extends  through  the  lamp  body 
to  the  top  of  d.  In  other  respects, 
the  Stokes  lamp  corresponds  to  the 
Clowes  hydrogen  lamp,  except  that  the  alcohol  flame  is  not 
as  persistent  as  the  hydrogen  flame  of  the  Clowes  lamp,  but 
is  more  easily  extinguished  in  gas;  the  flame  is  not  as  quickly 
extinguished  by  gas,  however,  as  the  oil  flame,  although  it 
is  more  easily  blown  out  by  wind.  The  lamp  is  designed  for 
the  detection  of  the  lower  percentages  of  gas,  varying  from 
i  per  cent,  to  3  percent.  Like  other  Gray  lamps,  it  is  not  a 
safe  lamp  in  the  presence  of  larger  percentages  of  gas. 


FIG.  14 


52 


MINE  GASES 


§6 


69.  The  Pleler  lamp  is  another  form  of  special  lamp 
designed  for  testing  for  gas.  It  has  the  form  of  a  large 
"tin-can  Davy,"  or  a  "Davy  in  case."  It  is  constructed  to 
burn  alcohol.  This  lamp  is  provided  with  a  higher  gauze 
than  any  other  type  of  lamp,  to  per- 
mit of  the  observance  of  the  high 
flame  caps  formed  over  the  alcohol 
flame,  which  is  extremely  sensitive  to 
gas.  A  perspective  view  of  this  lamp 
is  shown  in  Fig.  15.  The  alcohol 
flame  is  adjusted  in  fresh  air,  so  that 
its  tip  just  reaches  the  lower  edge  of 
the  window  in  the  bonnet  of  the  lamp. 
The  scale  for  reading  the  percent- 
ages of  gas  indicated  by  the  various 
heights  of  the  flame  cap  is  marked  on 
the  case  on  each  side  of  the  window 
or  on  the  window  itself.  The  lamp 
shown  in  the  figure  is  designed  to 
read  percentages  of  gas  varying  from 
i  per  cent,  to  li  per  cent.  Some 
Pieler  lamps,  provided  with  a  gauze 
measuring  8  inches  in  height,  allow 
the  observance  of  2  per  cent,  of  gas; 
when  more  gas  is  present  the  lamp  fills  with  flame.  The 
Pieler  lamp  is  by  no  means  a  safe  lamp  for  mine  use,  and 
would  be  almost  certain  to  cause  an  explosion  if  brought  into 
contact  with  a  body  of  explosive  gas. 


FIG.  15 


SAFETY-LAMP    DETAILS 

70.  Locks  for  Safety  Lamps. — All  safety  lamps  should 
be  securely  locked  to  avoid  the  possibility  of  their  being 
opened  in  the  mine.  If  for  any  reason  a  fire  boss  or  foreman 
carries  an  unlocked  lamp,  he  should  not  allow  it  to  pass  out 
of  his  hands  while  in  the  mine.  There  are  three  general 
plans  pursued  with  reference  to  the  locking  of  safety  lamps. 
These  embody:  (1)  a  simple  screw  pin,  or  other  catch  that 


§6  MINE  GASES  53 

will  prevent  the  lamp  being  opened  accidentally,  but  which 
may  be  opened  by  any  person  possessing  an  ordinary  amount 
of  ingenuity;  (2)  a  lock  that  can  be  opened,  but  will  reveal 
the  slightest  attempt  to  tamper  with  it;  (3)  a  lock  that 
cannot  be  opened  outside  of  the  lamp  room  or  relighting 
station. 

Although  all  safety  lamps  were  formerly  locked  in  the  first 
manner,  this  kind  of  lock  is  rapidly  falling  into  disuse,  as 
being  wholly  unsafe  in  a  gaseous  mine  where  a  large  number 
of  safety  lamps  are  in  use.  The  second  class  of  locks  repre- 
sents by  far  the  majority  of  those  in  common  use.  Although 
locks  belonging  to  this  class  can  be  opened  in  the  mine,  they 
do  not  easily  get  out  of  order,  and  are  extensively  used  on 
account  of  their  cheapness  and  simplicity  of  construc- 
tion. In  the  use  of  these  locks,  the  discipline  of  the  mine 
should  be  such  as  to  go  very  far  toward  preventing  any  one 
from  tampering  with  them  or  in  any  way  attempting  to 
open  a  lamp. 

71.  The  lead-plug  lock,  which  belongs  to  the  second 
class  and  has  the  general  form  shown  in  Fig.  16,  is  perhaps 
the  most  common  lock  in  use;  it  is  a  good  lock  for  cheapness 
and  security,  allowing  the  lamp  to  be  quickly  locked  or  opened, 
and  revealing  with  certainty  any  attempt  on  the  part  of  the 
miner  to  open  the  lamp.  It  is  important  that  the  date  or  a 
given  letter  should  be  stamped  on  the  lead  plug  each  day, 
and  means  should  be  adopted  to 
prevent  the  stamp  used  for  this 
purpose  being  duplicated  by  any 
one  employed  in  or  about  the  mine. 
As  shown  in  the  figure,  the  lower 
part  of  the  lamp  is  encircled  with  a 
movable  ring  R,  to  which  is  at-  FlG-16 

tached  a  hinged  lock  that  drops  over  a  projecting  lug  attached 
to  the  oil  vessel.  The  lead  plug  is  inserted  through  a  hole 
in  this  lug  and  punched  flat  to  prevent  its  removal.  The 
punch  used  stamps  the  date  or  letter  for  the  day  on  the 
plug.  The  lamp  is  opened  in  the  lamp  room  or  relighting 


54 


MINE  GASES 


station  by  cutting  the  plug,  the  lead  being  saved  and  remelted 
for  use  again. 

72.  Another  form  of  lock  belonging  to  the  second  class 
is  that  formerly  used  in  what  were  known  as  the  "Protector" 
lamps.  This  lock  is  shown  in  section  and  detail  in  Fig.  17. 
The  wick  tube  a  is  provided  with  a  screw  thread  that  allows 
a  collar  b  having  two  flanges,  as  shown  in  perspective  at  (a), 
to  be  screwed  over  it;  this  is  done  before  lighting  the  lamp. 
The  lamp  is  then  lighted  and  after  being  trimmed  is  screwed 
into  place.  The  flange  tube  c  is  then  fastened  by  pushing  in 
the  bolt  d,  which  is  provided  with  a  spring,  as  shown  at  (a), 

that  prevents  the  bolt  being 
withdrawn  until  the  oil  vessel 
is  removed.  It  will  be  ob- 
served that,  while  the  oil  ves- 
sel may  easily  be  unscrewed, 
the  flange  tube  cannot  be  re- 
moved, but  must  remain  sta- 
tionary in  the  lamp  until  the 
bolt  d  is  drawn  back.  As  a 
result,  any  attempt  to  unscrew 
the  oil  vessel  will  cause  the 
ef  lamp  to  be  extinguished  by 
its  wick  being  drawn  down 
through  the  collar  or  flange 
tube  c. 

73.     The  magnetic  locks 

that  have  been  used  on  some 
safety  lamps  belong  to  the 
third  class.  When  properly  constructed,  such  a  lock  cannot 
be  opened  outside  of  the  lamp  room  or  relighting  station, 
where  a  powerful  magnet  is  kept.  These  locks  consist  of 
a  pin  or  lever  that  slips  into  a  recess  in  the  oil  vessel  and 
is  kept  there  by  a  spring,  until  a  magnet  is  applied  to  the 
outside  of  the  lamp  and  the  pin  or  lever  is  drawn  out  of  the 
recess,  when  the  oil  vessel  can  be  unscrewed.  Some 
forms  of  magnetic  locks  can  be  opened  by  a  sudden  jar 


§6 


MINE  GASES 


55 


or  blow  on  one  side  of  the  lamp,  the  oil  vessel  being 
turned  at  the  moment  the  blow  is  given,  but  this  defect  can 
be  overcome  by  the  use  of  a  spring  of  sufficient  strength. 

Fig.  18  shows  a  magnetic  lock  that  is  in  very  successful 
use  in  connection  with 
the  Wolf  lamp.  A  key  a 
on  the  end  of  the  lever 
pivoted  at  the  center  is 
pressed  inwards  by 
means  of  a  spring  b,  so 
that  it  runs  in  the  thread 
of  the  oil  well  when  this 
is  screwed  up,  and  when 
it  is  in  place  drops  into  a 
socket  and  thus  securely 
locks  the  lamp.  The 
lock  mechanism  is  pro- 
tected by  a  hardened- 
steel  plate  c  on  the  outside  of  the  ring.  To  open  the  lock, 
two  poles  d,  e  at  the  ends  of  this  ring  are  placed  against  the 
poles  /,  g  of  a  horse-shoe  magnet,  as  shown,  which  draws  the 

key  a  from  its  seat  in 
the  oil  vessel  and  per- 
mits the  bottom  of  the 
lamp  to  be  unscrewed. 
If  a  weak  spring  is 
used,  the  lamp  may  be 
unlocked  with  a  hand 
magnet;  but  a  spring 
of  such  strength  is 
generally  used  that  a 
powerful  magnet  is 

__  required,   such  as  is 

shown  in  Fig.  19.     In- 
stead of  a  permanent 
magnet,    an    electro- 
magnet suitably  connected  with   the  electric   current  used 
about  the  mine  may  be  employed. 


56  MINE  GASES  §6 

74.  Lamp  Wicks,  Wick  Tubes,  Etc. — A  better  light 
will  usually  be  obtained  by  using  a  short  wick  and  renewing 
it  often,  than  by  employing  a  long  wick  for  a  greater  period 
of  time.     The  wick  is  round  or  flat  according  to  the  kind  of 
wick  tube  used;  a  round  wick  is  composed  of  several  strands 
of  cotton  yarn  very  slightly  twisted.     A  little  practice  will 
show  the  size  of  wick  or  number  of  strands  that  should  be 
used  to  give  the  best  results  with  each  kind  of  oil.     It  is 
important  that  the  wick  should  not  fit  so  tightly  in  the  wick 
tube  as  to  obstruct  the  free  flow  of  the  oil  to  the  flame. 
When  a  flat  wick  is  used,  the  thickness  and  width  of  the 
wick  should  only  be  slightly  greater  than  the  inside  dimen- 
sions of   the  wick   tube.     A  flat  wick  consists  of   several 
strands  of  cotton  yarn  plaited  very  loosely  together.     Lamp 
wicks  should  always  be  thoroughly  dried  before  being  placed 
in  the  lamp,  since  the  slightest  moisture  in  the  wick,  impedes 
the  flow  of  the  oil  and  lessens  the  light. 

75.  The  -wick  tube  of  a  lamp  is  made  either  round  or 
flat,  both  forms  being  in  common  use.     A  flat  wick  tube 
should  be  corrugated  on  one  side,  to  reduce  the  friction  and 
give  proper  air  space  in  the  tube.     The  top  of  the  tube,  when 
the  lamp  is  screwed  in  place,  should  be  about  i  inch  above 
the  lowest  sight  line  of  the  glass  chimney.     If  the  flame  sets 
too  low  in  the  lamp,  the  shadow  cast  on  the  ground  by  the 
body  of  the  lamp  is  increased;  and  if  the  flame  sets  too  high 
in  the  lamp,  its  luminosity  will  be  decreased.     The  wick  tube 
is  provided  on  one  side  with  a  narrow  slot  to  allow  the  wick 
to  be  raised  by  the  picker.     This  slot  should  not  be  wider 
or  longer  than  necessary  for  this  purpose,  as  the  heat  of  the 
lamp  will  then  cause  vaporization  of  the  oil  at  this  point, 
decreasing  the  flow  of  oil  to  the  flame;  and  the  wick  may 
become  ignited  at  the  slot. 

76.  The  purpose  of  the  picker  is  to  cleanse  the  wick 
from  time  to  time  of  the  incrustation  caused  by  the  imper- 
fect burning  of  the  oil  and  the  wick.     The  incrustation  is 
greater  when  a  poor  oil  is  used;  also  with  some  vegetable 
oils  than  with  most  animal  oils;  and  generally  greater  with 


§6  MINE  GASES  57 

vegetable  and  animal  oils  than  with  the  lighter  mineral  oils. 
The  usual  form  of  picker  permits  but  one  half  of  the  wick 
of  the  lamp  to  be  cleansed,  and  it  is  often  difficult  or  impos- 
sible to  free  the  other  half  of  a  wick  of  a  closed  lamp  from 
the  adhering  incrustation.  Owing  to  a  poor  picker,  it  is  often 
difficult  to  trim  a  closed  lamp  without  extinguishing  the  flame; 
the  flame  is  often  extinguished  also  by  the  awkward  handling 
of  the  picker.  The  best  form  of  picker  should  sweep  the 
entire  top  of  the  wick  with  a  motion  somewhat  inclined  to 
the  horizontal. 

77.  The  gauze  may  be  made  of  iron,  copper,  or  brass 
wire,  but  an  iron  gauze,  being  the  least  fusible,  is  considered 
the  safest,  and  the  use  of  copper  and  brass  gauze  should  be 
restricted  to  working  lamps,  in  which  the  gauze  is  not  apt  to 
be  exposed  to  a  flame. 


OILS    FOR    SAFETY    LAMPS 

78.  The  oils  commonly  used  in  safety  lamps  are  of  three 
general  classes:  vegetable  oils,  animal  oils,  and  mineral  oils. 

79.  The  vegetable  oils  most  commonly  used  for  mining 
purposes  are  cottonseed  and  rape,  or  colza,  oils.     The  latter, 
used  in  Europe,  are  derived  from  the  seed  of  a  variety  of 
turnip  largely  cultivated  for  this  purpose.     The  summer  rape 
is  often  called  colza,  whence  the  name  colza  oil;  the  name 
cabbage-seed  oil  has  also  been  applied  to  this  oil.     Rape,  or 
colza,  oil  is  a  safe  oil  for  mining  use,  but  its  illuminating  power 
is  not  as  great  as  that  of  petroleum  or  mineral  oil.     The 
poorer  qualities   of  this  oil  cause  considerable  incrustation 
of  the  wick  in  burning,  and  they  do  not  feed  as  readily  as  the 
lighter  mineral  oils.     The  best  grade  of  colza  oil,  however, 
has  long  been  a  favorite  in  certain  localities  for  use  in  safety 
lamps.     The  oil,  after  being  pressed  out  of  the  rape,  or  colza, 
seed,  is  purified  by  treatment  with  sulphuric  acid,  which  car- 
bonizes or  burns  out  much  of  the  organic  matter  contained 
in  the  oil  as  an  impurity;  the  oil  is  then  washed  to  cleanse  it 
from  the  acid. 


58  MINE  GASES  §6 

80.  The  animal  oils  used  in  lamps  are  seal  oil,  pressed 
out  of  the  blubber  or  fat  of  the  seal;  whale  oil,  obtained  from 
the  blubber  of  the  whale;  and  lard  oil,  obtained  from  the  lard 
secured  by  refining  hog  fat.     Lard  oils  are  now,  perhaps,  the 
animal  oils  most  commonly  used  in  safety  lamps.     Animal 
oils,  like  vegetable  oils,  do  not  possess  a  high  illuminating 
power;  much  depends  on  the  purity  of  the  oil.    A  good  qual- 
ity of  lard  oil  or  whale  oil  does  not  incrust  the  wick  rapidly. 

The  illuminating  power  of  both  vegetable  and  animal  oils 
may  be  increased  and  the  incrustation  of  the  wick  decreased 
by  the  addition  of  one-half  their  volume  of  petroleum;  the 
tendency  of  the  flame  to  smoke,  however,  is  somewhat 
increased,  and  the  mixture  burns  more  rapidly. 

81.  Mineral  oil,  or  petroleum,  is  obtained  from  the 
earth   by  boring   holes    from    the    surface   into    oil-bearing 
strata.     When  the  crude  petroleum  obtained  from  the  oil 
well  is  heated,  a  number  of  volatile  products  are  distilled 
from  it.     The  products  that  come  off  below  302°   F.   are 
known   as   the   light  oils.     Between  302°  and  572°   F.,   the 
biirning  oils  (or  kerosene)  are  given  off.     At  this  higher  tem- 
perature there  still  remain  the  heavy,  or  lubricating,  oils  and 
the  solid  ingredients  of  the  oil,  such  as  tar,  wax,  etc.     There 
are  a  large  number  of  the  light  oils,  and  the  ones  commonly 
used  are  gasoline,  naphtha,  and  benzine.     The  exact  tempera- 
tures between  which  each  of  these  several  oils  is  given  off 
vary  considerably  for  crude  oils  of  different  composition  and 
according  to  different  authorities,  but  for  the   present  pur- 
pose it  will  be  sufficient  to  assume  that  gasoline  is  distilled 
at  from  65°  to  140°  F.,  naphtha  at  from  140°  to  230°  F.,  and 
benzine  at  from  230°  to  302°  F.     The  more  volatile  of  these 
light  oils  should  not  be  used  for  burning  purposes,  as  they 
are  dangerous.     The  naphtha  that  is  sold  for  burning  pur- 
poses is  generally  a  product  distilled  at  from  212°  to  302°  F. 

82.  The  report  of   the    British   Accidents   Commission 
made  some  years  ago  was  unfavorable  to  the  use  of  benzine 
and  naphtha  in  safety  lamps,  as  these  oils  were  said  to  pro- 
duce a  flaring  flame,  which  increased  the  danger  if  the  lamp 


§6  MINE  GASES  59 

reservoir  became  warm.  The  report  of  this  commission 
has  created  a  prejudice  against  the  use  of  naphtha,  in  the 
minds  of  many,  which  does  not  seem  to  be  justified  by  later 
experiments  made  under  the  auspices  of  the  German  govern- 
ment, and  more  recently  by  government  officials  in  Belgium. 
These  latest  Belgian  tests,  reported  in  1904,  show  that  as 
the  result  of  many  thousands  of  experiments,  made  both  in 
the  laboratory  and  in  the  mines  under  working  conditions, 
less,  volatile  of  the'  light  oils  should  not  be  considered  dan- 
gerous. The  same  tests  also  showed  that  dust  in  the  mine 
air  does  not  materially  affect  the  safety  of  a  lamp. 

The  conclusions  of  the  British  Accidents  Commission 
briefly  stated  are  as  follows:  (1)  Rape  (colza)  oil  of  good 
quality,  burned  alone  in  a  safety  lamp,  incrusts  the  wick  after 
a  brief  period  of  time.  (2)  Good  clear  seal  oil  is  superior 
to  rape  (colza)  oil  in  maintaining  a  uniform  height  of  flame 
for  a  longer  period  of  time  without  trimming.  (3)  The 
addition  of  one-half  volume  of  petroleum  having  a  flashing 
point  of  80°  F.,  to  a  refined  rape  (colza)  oil  of  good  quality, 
greatly  improved  its  burning  qualities  and  lessened  the 
incrustation  of  the  wick,  but  the  luminosity  of  the  flame  was 
not  materially  increased;  when  one  volume  of  the  petroleum 
was  added,  the  flame  maintained  a  uniform  height  for  a 
longer  period  of  time,  anjd  its  luminosity  was  somewhat 
increased.  (4)  A  like  addition  of  one-half  volume  of  petro- 
leum to  a  seal  oil  of  good  quality  increased  the  length  of 
time  during  which  the  flame  maintained  a  uniform  height, 
and  improved  its  luminosity;  when  the  addition  of  petroleum 
to  seal  oil  was  increased  to  one  volume,  the  length  of  time 
the  flame  maintained  a  uniform  height  was  greatly  increased 
and  its  luminosity  improved,  but  the  consumption  of  oil  and 
wick  was  also  considerably  increased.  The  refined  p'etro- 
leum  used  for  this  purpose  is  the  last  of  the  products  of 
distillation  mentioned  previously,  and  is  commonly  known  as 
kerosene,  or  coal  oil. 

83.  The  flashing  point  of  petroleum  for  use  in  a  safety 
lamp— that  is,  the  temperature  at  which  the  oil  gives  off 


60 


MINE  GASES 


explosive  vapors — should  not  in  any  case  fall  below  73°  F., 
while  the  minimum  flashing  point  of  this  oil  recommended 
by  many  is  80°  F.  The  flashing  point  of  any  oil  may  be 
roughly  determined  by  placing  a  sample  of  the  oil  in  a  small 
vial  uncorked,  and  introducing  the  vial  into  a  vessel  of  hot 
water  in  which  a  thermometer  is  placed.  As  the  temperature 
of  the  water  is  gradually  raised  by  the  application  of  heat  to 
the  vessel,  the  point  at  which  vaporization  of  the  oil  takes 
place  is  determined  by  holding  a  match  over  the  mouth  of 
the  vial  and  noting  when  the  vapor  inflames. 

TABLE  VIII 


Illuminant 

Relative 
Volumes  of 
Oils  Mixed 

Light 
Value 

Remarks 

Standard  candle    

I.OO 

Rape  oil  (English)    

.32 

Colza  oil  (best  quality)    .    .    . 
Seal  oil    

-47 
•  35 

fRape  oil  (English)    
1  Royal  daylight  petroleum  .    . 
Safetv-lamp  oil 

3 

•30 
«1 

Safety-lamp  oil  .    

•4.5 
38  \ 

Different 

Safety-lamp  oil 

'    1 

ci 

makers 

•31  J 

84.     Relative   Illuminating  Powers   of    Oils. — It  is 

perhaps  unfair  to  compare  the  illuminating  powers  of  different 
oils  by  burning  them  in  the  same  lamp,  since  some  of  the 
oils  may  be  better  adapted  to  the  lamp  used  than  others. 
Table  VIII  gives  the  relative  illuminating  power  of  several 
oils  in  common  use  when  burned  in  a  common  Clanny  lamp, 
referred  to  a  standard  candle  as  unity.  This  standard  candle 
burns  120  grains  of  spermaceti  per  hour.  The  results  given  in 
Table  VIII  are  the  averages  of  numerous  determinations,  and 
can  only  be  taken  as  suggestive  of  the  light  value  of  the  oil,  as 
these  values  .for  the  same  kind  of  oil  vary  widely  according 
to  the  quality  of  the  oil  and  the  manner  in  which  it  is  burned. 


MINE  GASES 


61 


85.  The  Relative  Illuminating  Power  of  Safety 
Lamps. — The  illuminating  power  of  a  safety  lamp  depends 
more  on  the  construction  of  the  lamp  than  on  the  kind  of  oil 
burned.  Table  IX  is  of  interest  as  giving  the  average  illu- 
minating power  as  determined  by  a  large  number  of  tests  of 
different  kinds  of  safety  lamps  burning,  for  the  most  part, 
rape,  colza,  or  seal  oil. 

TABLE   IX 


Name  of  Lamp 

Illuminating  Power 
Standard  Candle  =  i 

Davy  (common)     

,13 

Davy  (Jack)    

.08 

Davy  (in  case)    

.16 

Clanny      .    . 

.•»4 

Mueseler  (Belgian)    

•  32 

Mueseler  (English)    .    .        

.36 

Gray 

.74 

Evan  Thomas     ....        

.4? 

Marsaut  (three  gauzes)        ...... 

•45 

Marsaut  (two  gauzes)                               .    . 

.cc 

Marsaut  (with  Howat's  deflector)      .    .    . 
Ashworth-Hepplewhite-Gray  
Wolf  (burning  naphtha)  

.65 
.65 

1.  00 

The  values  given  in  Table  IX  are  only  suggestive  and 
fairly  comparative,  as  the  difference  in  the  illuminating 
powers  of  lamps  of  the  same  type  is  very  wide,  and  the 
values  given  are  merely  the  average  values  for  each  type. 


145—10 


62  MINE  GASES  §6 

TESTING   FOR   GAS 


TESTING    FOR    GAS    WITH    THE    DAVY    LAMP 

86.  The  universal  method  of  testing  for  gas  in  mine 
air  is  by  means  of  the  flame  of  the  safety  lamp.  Although 
the  expression  testing  for  gas  may  refer  to  the  detection  of  the 
presence  of  any  of  the  mine  gases,  marsh  gas  (methane)  is 
nearly  always  meant.  The  manner  of  making  the  test  with 
the  Davy  lamp  is  as  follows:  Holding  the  lamp  in  an  upright 
position  in  one  hand,  and  with  the  other  screening  the  eyes 
from  the  body  of  the  flame,  the  miner  slowly  raises  the  lamp 
toward  the  roof,  observing  the  flame  carefully  to  detect  the 
first  appearance  of  a  flame  cap  that  indicates  the  presence  of 
gas.  On  the  first  appearance  of  a  cap,  the  lamp  is  promptly 


Roof  Line 

=~  =-=^=^=^=^—_   Thjn  iayers  of  sharp  aas  c/ose  to  roof 

'  ~   ~ -~"  Layers  of  etplosivem/xtvretfire  damp* 
first  appearance  of  fas  /n  Davy 

eoj. 

toosmaM 
Day. 


but  slowly  withdrawn  from  the  gas,  noting  the  distance  of 
the  lamp  from  the  roof  when  the  flame  cap  appears. 

As  marsh  gas  (methane)  is  lighter  than  air,  it.  is  often 
found  more  or  less  stratified  at  the  roof,  particularly  if  the 
gas  is  issuing  from  the  roof  instead  of  from  the  floor  and  if 
the  air-current  is  not  very  strong.  It  is  customary  therefore 
to  report  the  depth  of  a  body  of  gas  at  the  roof,  in  inches 
or  feet. 

This  condition  will  be  made  more  clear  by  referring  to 
Fig.  20,  in  which  the  horizontal  dotted  lines  indicate  the 
decreasing  percentage  of  gas  downwards.  The  heavy 
dotted  line  marked  2.5%  indicates  the  lowest  position  in 


§6  MINE  GASES  63 

which  gas  would  be  detected  by  the  Davy  lamp.  With  a 
more  delicate  means  of  testing,  gas  would  be  detected  lower 
down  from  the  roof. 

87.  When    the    gas    is    issuing   from   the    floor   of    the 
workings,  even   the    air   is  quiet   in    a   room    or  chamber, 
the    conditions  will  be  materially  changed  from  those  just 
described.     The  diffusion  of  the  gas  as  it  rises  from  the  floor 
is  more  rapid,  and  much  of  the  gas  is  carried  off  in  what  air  is 
passing  in  the  place;  the  gas  is  less  stratified  and  there  is  no 
layer  of  nearly  pure  gas  at  the  roof.     The  conditions  with 
respect  to  testing  are  much  less  dangerous  than  in  the  former 
case,  where  the  gas  at  the  roof  may  enter  and  fill  the  top  of 
the  lamp;  and  when  the  latter  is  being  withdrawn  the  entry 
of  fresh  air  below  may  create  a  highly  explosive  condition 
of  the  air  in  the  lamp  and  cause  a  violent  internal  explosion 
that  may  be  communicated  to  the  body  of  gas  outside  of  the 
lamp.     When    the   gas  comes   from   the  floor  and   diffuses 
upwards,  there  is  generally  a  more  uniform  percentage  of 
gas  indicated  in  any  position  of  the  lamp  between  the  roof 
and  the  floor. 

88.  Approaching  a  Body  of  Gas. — The  movement  of 
a  person  entering  a  chamber  in  which  there  is  gas  near  the 
roof  often  disturbs  this  layer  of  gas,  and  causes  it  to  descend 
and  surround  him  before  he  is  aware  of  its  presence.     On 
this  account,  great  care  is  required  in  entering  a  chamber 
when  the  gas  is  coming  from  the  roof  or  when  there  is  an 
opportunity  for  the  accumulation  of   a  body  of  gas  in  the 
roof.     It  is  always  more  dangerous  to  approach  a  body  of 
gas  on  the  intake  side,  where  the  fresh  air  creates  a  highly 
explosive  condition,  than  to  approach  the  same  body  of  gas 
on  the  return  side,  where  the  diffusion  is  greater  and  the 
change  to  a  dangerous  explosive  condition  less  abrupt. 

An  explosion  of  gas  inside  the  lamp  is  almost  certain  to 
take  place  when  the  lamp  is  withdrawn  from  a  body  of  gas 
into  fresh  air.  Such  an  internal  explosion  may  or  may  not 
be  communicated  to  a  body  of  gas  surrounding  the  lamp, 
according  to  the  security  afforded  by  the  lamp.  The  lamp 


64  MINE  GASES  §6 

in  which  an  explosion  has  taken  place  may  be  moved  slowly 
toward  the  feeder  of  gas  until  the  gas  filling  the  lamp  nearly 
extinguishes  the  flame,  when  the  lamp  may  be  slowly  with- 
drawn without  disastrous  results.  With  a  bonneted  lamp,  the 
danger  from  internal  explosion  on  withdrawing  the  lamp 
from  a  body  of  gas  is  greater  than  with  an  unbonneted  lamp, 
owing  to  the  restricted  circulation  in  the  lamp,  but  the 
security  afforded  by  the  former  lamp  against  the  transmis- 
sion of  the  explosion  is  greater. 

89.  Height  of  Flame  Cap  Corresponding  to  Differ- 
ent Percentages  of  Gas. — The  height  of  the  cap  formed 
above  a  flame  burning  in  air  containing  marsh  gas  (methane) 
indicates,  approximately,  the  percentage  of  gas  in  the  air, 
as  the  flame  cap  is  caused  by  the  ignition  of  this  gas.  A 
standard  flame  adopted  for  any  purpose  is  a  flame  burning  a 
known  weight  of  a  certain  combustible  in  a  unit  of  time; 
thus,  a  standard  candle  has  been  assumed  as  a  candle  burn- 
ing 120  grains  of  spermaceti  per  hour.  A  standard  flame, 
therefore,  represents  a  certain  amount  of  gas  burned  per 
unit  of  time.  The  flames  of  different  illuminants  are  not 
equally  sensitive  to  gas. 

Table  X  gives  the  heights  of  the  flame  caps  corresponding 
to  different  percentages  of  marsh  gas  (methane)  contained 
in  the  air  supporting  the  flame.  The  heights  of  the  flame 
caps  given  in  this  table  for  an  oil  flame  were  determined 
with  the  flame  reduced  to  about  i  inch  or  »  inch,  or  less, 
which  is  the  height  most  commonly  used  in  testing.  The 
heights  of  the  caps  obtained  will  vary  somewhat  from  those 
given  in  Table  X,  according  to  the  original  height  of  the 
flame,  but  a  flame  smaller  than  i  to  i  inch  is  apt  to  be 
extinguished  when  introduced  into  gas,  and  is  not  often  used. 

The  flame  of  burning  hydrogen,  as  shown  by  Table  X,  is 
the  most  sensitive;  although  alcohol  and  the  very  volatile 
oils  distilled  from  petroleum,  such  as  naphtha,  furnish  flames 
only  slightly  less  sensitive.  All  these  flames  give  caps  that 
are  clearly  perceptible  for  the  smaller  percentages  of  gas 
varying  from  i  to  3  per  cent.  The  naphtha  or  benzine  flame 


MINE  GASES 


65 


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66  MINE  GASES  §6 

permits  the  observance  of  caps  corresponding  to  smaller 
percentages  of  gas  than  is  possible  with  the  oil  flame,  and 
with  the  naphtha  flame  from  f  to  1  per  cent,  of  gas  is  quite 
easily  detected.  With  the  oil  flame,  however,  even  when 
drawn  to  its  lowest  possible  point,  only  the  most  experienced 
eye  can  detect  some  of  the  lower  caps  given  in  the  table. 
Experiments  have  shown  that,  for  sperm  oil,  the  height  of 
flame  cap  varies  as  the  cube  of  the  percentage  of  gas  con- 
tained in  the  air  mixture. 

Fig.  21  represents  the  heights  of  the  several  flame  caps 
corresponding  to  different  percentages  of  gas  as  they  appear 


25  3.O 

Percenfages  of  tSexa 

FIG.  21 

on  the  oil  flame.  In  the  use  of  the  oil  flame,  the  caps  below 
that  marked  2.5  per  cent,  cannot  ordinarily  be  discerned. 

Fig.  22  shows  the  corresponding  height  of  caps  from  the 
naphtha  flame,  the  heights  being  given  in  both  inches  and 
centimeters. 

The  alcohol  flame  used  in  the  Pieler  lamp  and  the  Stokes 
lamp  gives  the  largest  flame  caps  of  any  lamp;  that  in  the 
Pieler  lamp  being  5i  inches  in  height  for  2  per  cent,  of  gas. 
This  flame  is,  however,  easily  extinguished  by  a  slight  draft 
or  rapid  movement  of  the  lamp.  The  hydrogen  flame  of  the 
Clowes  lamp  is  usually  set  to  a  standard  height  of  I  inch,  for 


MINE  GASES 


67 


detecting  the  smaller  percentages  of  gas,  or  a  flame  f  inch  in 
height  may  be  used;  but  for  the  detection  of  the  higher  per- 
centages the  height  of  the  flame  must  be  reduced  to  i  inch. 


The  presence  of  carbon  dioxide  (carbonic-acid  gas)  does 
not  affect  the  formation  of  the  flame  cap  or  its  height, 
except  when  this  gas  is  present  in  sufficient  quantity  to  dim 
the  ordinary  flame  of  the  lamp. 


GAS   INDICATORS 

90.  Numerous  devices  have  been  employed  at  different 
times  for  indicating  the  gaseous  condition  of  the  mine  air. 
Most  prominent  among  these,  perhaps,  is  the  indicator 
devised  by  Mr.  Liveing,  which  depends  on  the  increased 
brilliancy  of  an  incandescent  coil  of  platinum  wire,  through 
which  a  current  of  electricity  is  passing,  when  the  wire  is 
surrounded  by  an  atmosphere  containing  marsh  gas  (meth- 
ane). The  incandescence  of  the  wire  ignites  the  gas  in 
contact  with  it,  and  the  heat  caused  by  the  combustion  of  the 
gas  increases  the  temperature  of  the  wire  and  causes  it  to 
glow  more  brightly,  the  brilliancy  increasing  with  the  per- 
centage of  gas  present. 


68  MINE  GASES  §6 

91.  The  Livelng  Indicator  consists   of  two  coils  of 
platinum  wire  of  equal  electrical  resistance.     One  of  these 
spirals  is  enclosed  in  a  tube  with  a  glass  cover  at  the  end 
facing  the  second  spiral;  this  tube  is  air-tight,  being  filled 
with  pure  air.     The  second  spiral  is  surrounded  by  a  cylin- 
der of  wire  gauze  having  a  glass  cover  at  the  end  facing  the 
first  spiral.     The  two  ends  of  the  cylinders  having  glass 
covers  are  4  inches  apart,  and  directly  between  them  is  a 
small  wedge-shaped  screen  or  mirror   so    arranged   as   to 
reflect  the  images  of  these  spirals  upwards  to  the  eye  of  the 
observer.     The  whole  is  enclosed  in  a  box  having  a  small 
glass  window  in  the  top,  through  which  the  incandescent 
spirals  are  observed.     By  means  of  two  rubber  tubes  attached 
to  the  box,  the  latter  may  be  filled  with  the  air  to  be  tested 
by  drawing  the  air  from  the  box  through  one  of  the  tubes, 
with  the  mouth  or  with  a  small  air  pump,  while  the  end  of 
the  other  tube  is  held  near  the  roof  or  where  gas  is  sus- 
pected.    In  the  bottom  of  the  box  is  a  small  magneto-elec- 
tric machine  for  generating  the  current,  and  which  is  operated 
by  turning  a  handle  on  the  side  of  the  box.     The  electric 
current  passing  through  both  of  the  platinum  coils  causes 
them  to  glow  with  equal  brilliancy  when  no  gas  is  present 
in  the  air  drawn  into  the  box.     If,  however,  this  air  contains 
gas,  the  spiral  enclosed  in  the  gauze  cylinder  will  glow  more 
brightly.     The  small  mirror  between  the  two  spirals  is  then 
moved  nearer  to  the  other  spiral  until  the  two  appear  of 
equal  brilliancy.     The  position  of  the  mirror  is  read  on  a 
scale  graduated  in  percentages,  and  by  this  means  the  per- 
centage of  gas  in  the  air  tested  is  determined.     This  indica- 
tor, although  cumbersome  and  expensive,  has  been  employed 
in  numerous  instances  for  the  examination  of  mine  workings. 

92.  The  Beard-Mackie  sight  Indicator  depends  on 
the  incandescence  of   fine  platinum  wires   suspended  in  a 
ladder-like  frame   above  the  flame  of  any  ordinary   safety 
lamp.     This  indicator,  which  is  shown  in  Fig.  23  attached  to 
a  common  Davy  lamp,  consists  of  a  No.  14  Birmingham  wire 
gauge  brass  wire  a  bent  in  the  form  of  an  inverted  U  and 


MINE  GASES 


69 


firmly  fixed  to  a  thin  brass  disk,  as  shown  in  Fig.  23  (a), 
fitting  into  the  neck  of  the  lamp,  and  held  firmly  in  a  vertical 
position  by  the  nipple  that  holds  the  wick  tube  in  place; 
sometimes  this  standard  is  attached  firmly  to  the  nipple 
itself,  as  shown  at  bt  Fig.  23  (£),  and  cannot  then  be 
detached  from  the  lamp  without  also  removing  the  nipple. 
On  this  standard,  fine  platinum  cross-wires  are  arranged  at 
such  heights  above  the  flame  as  to  indicate  by  their  incan- 
descence the  percentage  of  gas  present 
in  the  air.  The  indicator  thus  shows 
the  presence  of  gas  varying  in  amount 
from  i  per  cent,  to  3  per  cent.,  each 
successive  strand  of  platinum  wire 
showing  by  its  incandescence  an  in- 
crease of  i  per  cent, 
of  gas.  The  percent- 
age of  gas  indicated  by 
the  several  wires  is 
marked  opposite  each 
wire  in  Fig.  23  (a). 
This  indicator  may  be 
attached  to  the  lamp  or 
detached  as  desired. 
In  the  use  of  the  sight 
indicator,  the  flame  is 
first  adjusted  in  fresh 
air  to  such  a  height  that 
the  lowest  wire  of  the 
scale  only  is  aglow; 
this  is  called  the  stand- 
ard wire,  and  is  a  straight  platinum  wire.  The  percentage 
wires  are  looped,  which  makes  them  more  plainly  visible 
through  the  gauze. 

The  principle  on  which  the  sight  indicator  depends  may  be 
briefly  stated  as  follows:  The  combustion  of  the  marsh  gas 
(methane  or  light  carbureted  hydrogen),  which  is  the  chief 
constituent  of  firedamp,  produces  great  heat  but  little  light, 
the  flame  being  practically  non-luminous.  Platinum  wire 


PIG.  23 


70  MINE  GASES  §6 

possesses  the  property  of  absorbing  this  gas  to  a  greater  or 
less  extent,  and  is  thereby  rendered  more  sensitive  to  its 
presence;  the  incandescence  of  the  wire  makes  visible,  so  to 
speak,  the  heat  of  the  non-luminous  flame  cap  formed  by 
the  burning  gas.  It  is  well  known  that  this  flame  cap  is  not 
commonly  perceived  in  the  Davy  lamp  burning  ordinary  oil, 
even  when  the  flame  of  the  lamp  is  reduced  to  its  smallest 
size,  when  less  than  2i  per  cent,  of  gas  is  present,  and  many 
experienced  miners  have  difficulty  in  perceiving  the  cap  in 
3  per  cent,  of  gas.  By  means  of  the  indicator,  the  presence 
of  i  per  cent,  is  clearly  revealed  by  the  bright  incandescence 
of  the  lowest  wire  of  the  scale,  this  taking  place  with  the 
normal  working  flame  of  the  lamp.  Much  time  is  thus  saved 
in  making  a  test  for  gas,  as  it  is  not  necessary  to  draw  down 
the  flame  of  the  lamp  when  the  test  is  to  be  made.  The 
scale  of  incandescent  wires  also  affords  a  positive  reading, 
which  is  always  the  same  for  the  same  gaseous  condition  of 
the  air,  and  enables  an  intelligent  comparison  to  be  made 
between  the  reports  of  different  fire-bosses  in  different  sec- 
tions of  the  mine,  since  the  percentages  in  these  reports  are 
all  measured  by  the  same  standard. 

A  modified  form  of  the  indicator  just  described,  for  use  in 
the  working  lamp,  has  but  two  cross-wires  or  strands, 
adjusted  to  such  heights  as,  in  the  opinion  of  the  fire-boss, 
are  best  adapted  to  the  conditions  of  the  particular  mine 
where  the  indicator  is  to  be  used.  The  lower  of  these  two 
strands  is  called  the  warning  line,  and  it  gives  a  warning  of 
the  gaseous  condition  of  the  air;  the  upper  is  the  danger 
line,  and  indicates  a  point  where  all  naked  lamps  in  use 
should  be  extinguished.  The  position  of  both  the  warning 
line  and  the  danger  line  in  the  lamp  will  evidently  vary 
with  the  character  of  the  coal,  its  inflammability,  hardness, 
etc.  In  the  working  of  anthracite,  no  alarm  is  commonly  felt 
until  the  amount  of  gas  exceeds  2  per  cent.,  when  an  effort  is 
made  to  increase  the  ventilation  and  reduce  the  percentage 
of  gas.  In  the  working  of  bituminous  mines,  particularly 
where  there  is  dust  and  the  coal  contains  much  volatile 
matter,  the  danger  point  is  reached  at  a  lower  percentage. 


§6 


MINE  GASES 


71 


93.  The  Shaw  gas-testing  machine,  Fig.  24,  is  a 
simple  and  quite  accurate  mechanical  device  for  determining 
the  percentage  of  marsh  gas  (methane)  in  a  mixture  of  gas. 
On  account  of  its  size  and  lack  of  portability,  its  use  is 
restricted  to  laboratory  purposes,  and  it  cannot  replace  the 
method  of  testing  for  gas  at  the  working  face  by  means  of 
a  safety  lamp.  The  cylinders  a,b  are  fitted  with  pistons  that 
are  connected  to  the  lever  c  by  the  piston  rods  d,  <?,  the  rod  d 
being  permanently  attached  to  the  end  of  the  lever  c,  but 
the  end  of  e  being  movable  along  c.  The  cylinder  b  is  also 
movable  along  the  base  /,  which  is  graduated,  as  shown,  to 


FIG.  24 

correspond  with  graduations  along  c ,  so  that  when  b  is  placed 
at  a  certain  graduation  on  /,  the  upper  end  of  e  is  placed  at 
the  corresponding  graduation  on  c\  the  piston  rod  is  then 
clamped  firmly  by  the  clamp  screw  g  and  the  cylinder  b  by 
the  clamp  h.  By  means  of  the  handle  u,  the  gearing,  and 
the  rod,  the  short  end  of  the  lever  c  is  moved  up  and  down, 
and  in  this  way  the  pistons  within  a  and  b  are  caused  to  move 
up  and  down.  As  the  long  end  of  the  lever  c  rises,  the  piston 
connected  to  d  draws  air  into  the  cylinder  a,  while  the  pis- 
ton connected  to  e  draws  in  a  mixture  of  air  through  i  and  of 
gas  to  be  tested  through  j  into  the  cylinder  b.  The  relative 


72  MINE  GASES  §6 

amounts  of  air  drawn  into  a  and  of  the  gaseous  mixture  to 
be  tested  drawn  into  b  depend  on  the  relative  sizes  of  the 
cylinders  a  and  b  and  the  position  of  the  cylinder  b  on  the 
base  /  and  the  arm  c.  When  the  longer  end  of  the  lever 
arm  c  descends,  the  rod  k  turns  the  valve  /  so  that  the  open- 
ings into  i  and  j  are  closed,  and  at  the  same  time  it  opens 
the  valve  to  the  pipe  m,  which  connects  with  another  valve  n 
through  which  the  mixture  of  air  and  gas  from  the  cylin- 
ders a,  b  is  pumped  by  the  descending  pistons,  then  through 
a  pipe  underneath  the  base  and  up  through  the  tube  o,  into 
the  hollow  cylinder  p.  If  the  mixture  of  air  and  gas  in  p  is 
explosive,  it  is  fired  by  means  of  a  flame  from  the  burner  q 
through  the  opening  r,  which  connects  with  the  inside  of  p. 
Inside  the  cylinder  p  is  a  piston  that  is  driven  outwards  by 
an  explosion,  ringing  the  gong  s.  The  amount  of  gas  in  the 
explosive  mixture  is  determined  by  the  position  of  the  cylin- 
der b  as  given  by  the  readings  on  'the  arms  c  and  /,  the  per- 
centage for  the  various  readings  being  given  by  a  table 
furnished  with  the  machine. 

94.     Testing   for    Gas    by   the    Shaw    Machine. — In 

order  to  test  the  mine  air  for  gas  by  the  Shaw  machine, 
samples  of  the  air  must  be  collected  in  large  rubber  bags 
supplied  for  this  purpose.  The  bags  are  first  rolled  up  flat 
to  drive  out  all  the  air  they  contain;  the  mouth  of  the  bag 
is  then  held  at  the  roof,  or  wherever  it  is  desired  to  take  a 
sample  of  the  air,  and  the  bag  is  unrolled  and  expanded  by 
pulling  out  the  sides.  Sometimes  a  small  pump  is  used  to 
fill  the  bag  with  the  mine  air.  The  bag  containing  the  mine 
air  is  then  brought  to  the  surface  and  attached  to  the  small 
pipe  i  shown  on  the  right  of  the  distribution  box  /.  When 
the  valve  in  the  mouth  of  the  bag  is  opened  and  the  machine 
started,  the  air  from  the  bag  is  pumped  into  the  cylinder  a, 
instead  of  fresh  air  as  formerly;  if  this  air  contains  any  gas, 
it  is  evident  that  a  loud  explosion  will  be  caused  by  the 
mixture  pumped  into  the  combustion  chamber  p.  To  avoid 
this,  the  small  cylinder  pumping  pure  gas  is  set  back  a 
sufficient  distance  to  allow  for  the  supposed  percentage  of 


§6  MINE  GASES  73 

gas  contained  in  the  mine  air;  thus,  if  the  standard  gas  gave 
an  explosion  at  8  per  cent.,  and  the  mine  air  is  supposed  to 
contain,  say,  2  per  cent.,  the  small  cylinder  b  will  be  set  back 
to  8  —  2  =  6  per  cent,  on  the  upper  and  lower  scales.  If  an 
explosion  does  not  occur  in  this  position  of  the  cylinder,  it 
shows  that  the  mine  air  contains  less  than  2  per  cent,  of  gas, 
and  the  small  cylinder  is  then  advanced  slowly  till  an  explo- 
sion does  occur  when  the  machine  is  operated.  If  this 
explosion  occurs  at,  say,  6.5,  the  percentage  of  gas  in  the 
mine  air  is  8  —  6.5  =  1.5  per  cent. 

The  Shaw  gas  machine  is  valuable  and  accurate  as  a 
means  of  testing  the  percentage  of  gas  present  in  air,  but 
its  disadvantage,  ia  connection  with  the  testing  of  mine  air, 
is  the  inability  to  make  the  test  in  the  entry  at  the  point 
where  the  danger  exists.  By  the  time  the  mine  air  has  been 
bagged  and  carried  to  the  surface,  and  the  report  of  the  test 
returned  to  the  mine,  the  conditions  may  have  changed  and 
the  danger  passed  or  perhaps  largely  increased.  The  testing 
for  gas  in  the  mine,  to  be  efficient,  must  be  accomplished  at 
the  moment  and  at  the  point  where  the  danger  exists;  this 
can  only  be  done  by  a  portable  machine  or  lamp. 


8AFETY-I.AMP  HOUSES 

95.  Fig.  25  shows  a  very  convenient  lamp  house  as  used 
at  Heworth  Colliery,  England.  The  circular  and  revolving 
lamp  stands  a  are  placed  in  a  circle  around  the  cleaning 
machine  d,  and  by  this  arrangement  a  person  standing  at  the 
machine  can,  with  very  little  movement,  reach  any  safety 
lamp  in  the  house.  The  walls-of  the  cabin  are  circular  and 
18  inches  thick.  There  are  six  windows  c,  at  which  the 
lamps  are  handed  out  to  the  workmen,  and  two  stands  are 
conveniently  placed  adjacent  to  each  window.  The  entrance 
door  d  is  placed  at  one  end  of  the  building,  and  at  the  oppo- 
site end  there  is  a  door  leading  to  the  repair  shop  e.  Out- 
side the  wall  of  the  cabin,  and  4i  feet  distant  from  it,  is 
another  wall  9  inches  thick,  enclosing  a  passageway  tra- 
versed by  the  workmen  while  getting  their  safety  lamps. 


74 


MINE  GASES 


§6 


The  structure  is  covered  by  a  glass  roof,  so  as  to  obtain  a 
good  light.  The  floor  is  made  of  cement,  and  except  for  the 
windows,  doors,  and  cleaning  machine,  there  is  no  wood  that 
can  become  saturated  with  oil  or  catch  fire. 

The  double  lamp-cleaning  machine  b  is  driven  by  a  small 
steam  engine. 


The  oil  is  conveyed  in  pipes  from  the  storehouse  to  taps 
placed  at  each  end  of  the  cleaning  machine.  The  lamp  stands, 
shown  in  detail  in  Fig.  26,  are  made  of  wrought  iron  and 
hold  100  lamps  each.  There  are  five  pair  of  shelves  for 
each  stand,  one  shelf  /  of  each  pair  for  the  lamp  tops  being 
placed  back  of  and  slightly  higher  than  the  other  shelf  g, 


MINE  GASES 


76 


FIG.  '26 


which  is  for  the  bottoms. 
The  shelves  are  10i  inches 
apart,  and  the  lowest  one  is 
2i  feet  from  the  ground. 
The  tops  of  the  stands  are 
joined  by  a  ring,  and  the 
standard  of  each  stand  rests 
at  the  bottom  in  a  bearing 
that  is  cup-shaped,  so  as  to 
hold  oil. 

Two  men  only  on  each 
shift  are  authorized  to  lock 
the  lamps,  in  order  to  pre- 
vent an  unlocked  lamp  being 
given  out,  although  ten  men 
and  boys  are  employed  on 
each  shift  in  cleaning,  re- 
pairing, and  giving  out  the 
lamps. 

Each  workman  using  a 
safety  lamp  deposits  a  tag 
or  check  numbered  to  cor- 
respond to  the  number  on  his 
lamp  when  the  lamp  is  given 
to  him.  The  check  is  hung 
on  a  board  containing  hooks 
for  100  checks  and  placed 
beside  the  window  nearest 
the  lamp  stand  on  which  the 
lamp  is  stored.  Each  hook 
on  this  board  has  a  label  con- 
taining the  name  of  the  work- 
man and  the  number  of  his 
lamp,  and  by  inspection  of 
this  board  it  is  possible  to 
tell  who  is  in  the  mine.  If 
two  shifts  of  men  use  the 
same  lamps,  a  slate  is  hung 


76 


MINE  GASES 


between  the  boards,  with  the  names  of  the  men  or  the  dif- 
ferent shifts  on  opposite  sides. 

Lamps  needing  repairs  are  left  at  the  repair  room  e, 
Fig.  25,  instead  of  at  the  window  c. 

A  barometer,  thermometer,  and  copies  of  the  mining  laws 
and  any  special  colliery  regulations  are  placed  in  a  con- 
spicuous place  between  the  lamp  house  and  the  pit  head. 

96.  The  lamp  house,  of  which  Fig.  27  is  a  plan,  is  used  at 
the  Edenborn  mine  of  the  H.  C.  Frick  Coke  Company.  At 


this  mine,  Wolf  lamps  burning  naphtha  exclusively  are  used. 
The  walls  are  of  brick  surmounted  by  a  slate  roof.  A  is  the 
storeroom;  B,  the  lamp  room;  C,  the  office;  and  D,  the  room 
in  which  the  men  receive  and  return  the  lamps.  The  floor 
of  the  storeroom  and  lamp  room  is  of  cement  and  tile,  but 
that  of  the  office  is  of  pine.  In  the  lamp  room  are  a  number 
of  lamp  racks  a  with  hooks  attached  for  the  lamps,  each 
hook  being  numbered  and  reserved  for  the  lamp  bearing  the 


§6  MINE  GASES  77 

same  number.  The  two  slate-topped  tables  b  are  used  for 
cleaning  and  filling  the  lamps. 

The  cleaning  tables  are  fitted  with  powerful  magnets  for 
unlocking  the  lamps — the  Wolf  lamp  being  provided  with  a 
magnetic  lock — and  with  compressed-air  attachments  for 
blowing  the  dust  and  dirt  from  the  lamps. 

For  filling  the  lamps,  there  is  a  5-gallon  tank  on  the  clean- 
ing table.  This  tank  is  filled  by  a  pump  from  one  of  the 
tanks  or  barrels  in  the  storeroom  A,  only  enough  naphtha  to 
fill  the  lamps  required  for  use  being  kept  in  the  lamp  room. 
The  tank  is  equipped  with  an  automatic  attachment  for  filling 
the  lamps  without  overflowing  them. 

To  clean  the  lamps,  they  are  unlocked  and  the  globes, 
gauzes,  and  expansion  rings  removed.  The  cups  are  then 
put  under  the  filling  tap,  and  while  they  are  being  filled  the 
lampman  cleans  the  other  parts  by  means  of  compressed  air 
and  brass-wire  brushes  and  soft  cloths  to  polish  the  glasses. 

No  one  is  allowed  inside  the  lamp  house  except  such  per- 
sons as  are  required  to  care  for  and  distribute  the  lamps. 

The  men  receive  their  lamps  at  the  small  windows  c. 
Each  man  is  required  to  deposit  a  brass  check  with  his  num- 
ber stamped  on  it  before  he  is  given  a  lamp.  Each  lamp  is 
tested  before  being  given  out. 

When  the  lamp  is  returned,  the  man  receives  his  check 
back.  This  checking  system  shows  the  number  of  men  in 
the  mine  and  also  prevents  the  loss  of  lamps,  as  no  one  can 
get  his  check  unless  he  returns  a  lamp  or  can  give  a  satis- 
factory excuse  for  not  returning  it. 


PORTABLE   ELECTRIC  LAMPS 

97.  Many  unsuccessful  attempts  have  been  made  to  pro- 
vide an  electric  lamp  for  lighting  the  inner  workings  of  a 
mine.  For  numerous  reasons,  arc  lamps  are  not  adapted  to 
mine  work.  Incandescent  lamps  protected  by  strong  glass 
globes  have  been  used,  the  wires  conducting  the  current  from 
the  surface  to  the  lamps  being  usually  laid  on  the  floor  or 
buried  in  a  ditch  at  the  side  of  the  roadway.  These  lights, 

145—11 


78  MINE  GASES  §6 

however,  have  given  little  satisfaction,  owing  not  only  to 
their  stationary  character  and  the  dark  shadows  thrown  on 
certain  portions  of  the  work,  but  also  to  the  difficulty  of 
extending  the  lead  wires  from  time  to  time,  and  the  annoy- 
ance caused  by  these  wires  being  constantly  in  the  way.  So 
great  have  these  annoyances  proved  that  the  use  of  such 
lights  at  the  working  face  has  been  quickly  abandoned  wher- 
ever introduced.  Beside  the  annoyance  mentioned,  there  is 
always  present,  in  gaseous  mines,  the  danger  of  the  ignition 
of  the  gas  by  the  breaking  of  a  lamp.  The  numerous 
attempts  made  to  design  a  portable  electric  lamp  have  been 
but  little  more  successful,  the  difficulty  being  the  inability  to 
construct  in  a  lamp  of  moderate  weight  a  battery  capable  of 
yielding  a  suitable  light  for  a  period  of  at  least  8  or  10  hours 
at  a  time  without  recharging.  In  a  few  instances,  lamps 
have  been  made  that  would  yield  a  good  light  for  the  required 
length  of  time,  but  owing  to  their  weight  and  expense  they 
have  not  come  into  general  use. 

One  of  the  chief  objections  to  the  use  of  the  electric  light 
in  mine  workings  is  the  fact  that  such  a  light  affords  no  indi- 
cation of  the  gaseous  condition  of  the  mine  air  with  respect 
to  explosive,  poisonous,  or  suffocating  gases.  To  the  miner, 
this  is  almost  a  fatal  objection,  since  he  has  always  depended 
on  his  lamp  to  give  him  the  first  warning  of  a  dangerous 
condition  of  the  air. 


MINE  VENTILATION 

(PART  1) 

GENERAL    PRINCIPLES    OF    MINE    VEN- 
TILATION 


PRODUCTION    AND    CONTROL    OF    AIR-CURRENTS 


INTRODUCTION 

1.  The  subject  of  mine  ventilation  includes  the  various 
methods  and  appliances  for  producing  air-currents  in  a  mine 
and  for  conducting  a  sufficient  quantity  of  air  through  the 
mine  passages  and  workings.     The  purpose  of  this  air-cur- 
rent is  to  dilute,  and  thus  render  harmless,  the  noxious  gases 
given  off  from  the  coal  and  rock  strata,  and  also  to  sweep 
away  these  gases  and  those  resulting  from  blasting  and  the 
exhalations  of  the  men  and  animals.     It  is  necessary  that  the 
air  in  a  mine  be  constantly  changed,  because  men  and  animals 
cannot  live  and  lights  will  not  burn  without  an  adequate  and 
constant  supply  of  pure  air.     The  proper  ventilation  of  a 
mine  requires  that  a  sufficient  air-current  be  so  distributed 
throughout  the  workings  as  to  sweep  the  entire  working  face 
with  a  velocity  sufficient  to  dislodge  and  carry  away  the  gases 
that  accumulate  at  the  face  and  in  the  cavities  of  the  roof, 
and  often  also-  those  accumulating  in  places  that  have  been 
worked  out.  

CONDUCTING    AIR-CURRENTS 

2.  Definitions. — In  order  to  control  the  direction  and 
amount  of  the  air-currents  passing  through  a  mine,  some  of 
the  principal  means  employed  are  airways,  cross-cuts,  mine 

Copyrighted  by  International  Textbook  Company.    Entered  at  Stationers'  Ha  II,  London 

118 


2  MINE  VENTILATION  §13 

doors,  curtains,  regulators,  brattices,  stoppings,  and  air  cross- 
ings. The  term  a  mine,  as  here  understood,  refers  to  a 
system  of  underground  passageways  and  openings,  as  shown 
in  Fig.  1,  driven  for  the  most  part  in  the  seam  or  stratum  it 
is  desired  to  remove  and  connected  with  the  surf  ace 'by  a 
drift  or  tunnel,  which  is  a  horizontal  opening,  a  shaft, 
which  is  a  vertical  or  nearly  vertical  opening,  or  a  slope, 
which  is  an  inclined  opening. 

The  ventilation  of  a  mine  requires  an  air  current  passing 
through  the  mine.  An  air-shaft  is  a  shaft  sunk  from  the 
surface  to  the  mine  workings,  for  the  purpose  of  ventilation; 
a  downcast  shaft  is  a  shaft  by  which  air  enters  a  mine;  an 
upcast  shaft  is  one  by  which  the  return  air  is  discharged 
from  a  mine.  The  passageways,  shown  in  Fig.  1,  called 
gangways,  entries,  or  headings,  and  air-courses,  or 
airways,  furnish  a  way  out  of  the  mine  for  the  material 
mined,  and  a  way  into  the  mine  for  the  fresh  air  or  a  way 
out  for  foul  air  and  noxious  gases;  they  also  block  out  the 
mine  and  enable  the  coal  to  be  mined  at  a  number  of  points 
at  the  same  time.  To  provide  for  an  air-current  into  and 
out  of  the  mine,  the  passageways  are  generally  driven  in 
pairs.  The  passageway  by  which  the  air  is  conducted  into 
the  mine  is  called  the  intake,  and  the  one  by  which  the  air 
is  carried  out  of  the  mine,  the  return. 

Openings,  called  rooms  or  chambers,  are  turned  off  one 
or  both  sides  of  a  pair  of  passageways  or  entries.  The 
mouth  of  an  entry,  airway,  or  room,  is  its  outer  end 
or  opening.  The  innermost  ends,  or  faces,  of  all  entries 
and  rooms  are  the  working  places  of  the  mine,  where  the 
coal  is  mined.  The  face  of  a  room  is  sometimes  called  the 
breast  of  the  room;  the  side  wails  of  all  entries,  airways, 
and  rooms  are  called  ribs. 

Cross-cuts,  or  break-throughs,  are  openings  made  at 
regular  intervals  between  the  two  entries  of  a  pair,  or  between 
two  adjoining  rooms  to  conduct  the  air  from  the  intake  into 
the  return  entry,  or  from  room  to  room,  and  thus  keep  the 
air  in  circulation  at  all  the  working  faces  in  the  mine.  As 
shown  in  Fig.  1,  each  cross-cut  is  closed  by  building  an 


§13 


MINE  VENTILATION  3 

as   soon  as  a  cross-cut  is  made  near 


air-tight  stopping 
the  face. 

If,  for  any  reason,  a  single  entry  is  driven  instead  of  two 
entries,  the  air  is  carried  into  the  face  of  the  entry  and  then 
to  the  room  nearest  the  face  of  the  entry  by  a  brattice, 
which  is  a  partition  of  boards  or  canvas  placed  so  as  to 
divide  a  single  airway  into  two  parts,  one  for  the  incoming 
and  the  other  for  the  outgoing  air.  The  air  passes  up  the 


FIG.  1 

room  nearest  the  face  of  the  entry  and  along  the  faces  of  the 
tier  of  rooms,  and  is  then  carried  to  the  upcast  shaft  by  a 
special  airway  connecting  the  room  nearest  the  upcast  shaft 
with  the  upcast  shaft. 

3.  Mine  Doors. — To  deflect  the  air-current  from  the 
entry  in  which  the  door  is  placed  into  a  side  or  cross-entry 
or  passage,  mine  doors,  Fig.  2  (a),  are  generally  used;  these 


MINE  VENTILATION 


§13 


are  constructed  of  a  double  thickness  of  boards  made  to  cross 
each  other  diagonally  so  as  to  add  to  the  strength  of  the 
door.  The  door  is  hung  in  a  substantial  frame  made  of 
timber  firmly  wedged  between  the  floor  and  the  roof. 
Before  setting  the  door  frame,  the  sides  and  roof  of  the 
entry  are  dressed  so  as  to  form  a  good  bed  for  the  timbers 
and  proper  clearance  for  the  door.  The  door  should  be 
hung  on  the  side  of  the  frame  toward  the  direction  from 
which  the  air  comes,  so  that  the  force  of  the  air-current  will 
keep  the  door  closed.  Large  strap  hinges  are  bolted  to  the 
door  in  such  a  way  as  to  give  it  a  sufficient  fall  to  prevent  its 
standing  open.  To  do  this,  the  lower  staple  supporting  the 
end  of  the  hinge  is  set  in  the  door  frame  about  1*  inches 
farther  back  from  the  door  than  the  upper  staple.  If  the 


(a)  FIG.  2 

seam  has  a  slight  pitch,  as  shown  in  the  figure,  it  will  be 
necessary  to  cut  the  roof  so  as  to  give  the  proper  clearance 
to  the  door  when  it  is  open,  as  shown  in  Fig.  2  (b). 

4.  A  canvas  door,  or  curtain,  consists  of  a  piece  of 
canvas  hung  from  a  cross-bar  by  rings,  and  serves  the  pur- 
pose of  a  temporary  door  where  the  requirements  will  not  war- 
rant the  expense  of  a  timber  door.     A  canvas  door  or  curtain 
is  often  used  where  it  is  desired  to  turn  only  a  portion  of  the 
air-current,  as  the  air  that  leaks  through  the  curtain  ventilates 
the  passageway  beyond  the  curtain.     A  canvas  brattice  used 
to  deflect  the  air-current  to  the  face  of  a  room  is  shown  at  d, 
Fig.  1. 

5.  Regulators. — Any  device  constructed  in  an  airway  to 
divide  an  air-current  proportionately  between  two  airways  is 


13 


MINE  VENTILATION 


a  regulator.  There  are  two  forms  in  use,  known  as  the 
box  regulator  and  the  regulator  door.  The  box  regulator, 
Fig.  3,  consists  of  a  solid  board  stopping  a,  or  of  a  door,  with 
a  hole  cut  in  the  center  and  provided  with  a  shutter  b  that 


FIG.  3 

can  be  slid  over  the  opening  so  as  to  regulate  the  size  of  the 

opening  through  which  the  air  is  allowed  to  pass.     By  this 

means,  the  volume  of 

air  passing  through 

the  regulator  is  made 

greater  or  less,  as 

desired.     The  box 

regulator    is    usually 

placed  at   the  inby 

end  of  the  air-current 

that  it  controls,  on  an  Pl°-  4 

entry  or  air-course  that  is  not  used  as  a  haulage  road,  so  as 

not  to  interfere  with  the  passage  of  the  cars. 

The  door  regulator,  Fig.  4,  is  a  door  provided  with 
a  set  lock,  so  that  it  may  be  secured  in  any  desired  posi- 
tion. It  is  always  placed  at  the  mouth  of  an  entry,  and 


6  MINE  VENTILATION  §13 

is  so  arranged  that  it  may  be  swung  to  one  side  or  the 
other,  so  as  to  increase  or  decrease  the  quantity  of  air 
passing  in  either  entry.  The  angle  at  which  this  door  is 
set  and  the  amount  of  opening  left  in  the  box  regulator  are 
usually  ascertained  by  trial,  so  as  to  give  the  desired  divi- 
sion of  the  air  between  the  two  entries.  The  method  of 
calculating  the  amount  of  air  passing  through  a  regulator  will 
be  explained  later. 

6.  Brattices. — The  most  common  form  of  a  brattice  is 
the  board  brattice  shown  in  Fig.  1,  where  it  is  built  on  the 
return  airway  to  conduct  the  air-current  forward  to  the  face 
of  this  airway,  which  is  some  distance  ahead  of  the  face  of 
the  intake  airway.     It  would  be  impossible  to  ventilate  a 
single  airway  without  a  brattice   or  some    similar   device. 
This  brattice  is  built  by  setting  a  row  of  posts  in  the  airway, 
several  feet  from  one  rib,  and  nailing  boards  or  canvas  to 
them  so  as  to  form  an  air-tight  partition.     Brattices  are  also 
extensively  used  in  the  rooms  for  conducting  the  air  from 
the  last  cross-cut  to  the  face.    When  a  brattice  is  used,  it  is 
customary  to  carry  the  air  behind  the  brattice  and  allow  it  to 
return  on  the  roadway,  instead  of  carrying  the  air  in  on  the 
roadway  and  returning  it  behind  the  brattice. 

7.  Stoppings. — A  wall  built  to  close  off  an  airway  or  a 

break-through  is  called 
a  stopping.  A  common 
form,  Fig.  5,  consists  of 
two  loose  walls  of 
slate  a  a  few  inches 
apart  and  having  the 
space  between  filled 
^^mf^m^f  with  fine  dirt  or  sand. 
The  back  wall  of  slate  is 
FlG-  5  first  built  up  to  the  roof, 

and  the  front  wall  is  then  started,  the  space  b  between  the 
walls  being  filled  in  and  rammed  as  this  wall  is  built  up. 
Care  must  be  taken  to  pack  the  material  tightly  against  the 
roof  to  prevent  the  leakage  of  air  through  the  stopping. 


§13  MINE  VENTILATION  7 

There  is  no  economy  in  building  a  poor  stopping,  as  this 
causes  great  trouble  and  expense  in  the  future  working  of 
the  mine.  Stoppings  are  sometimes  built  of  concrete  or 
brick  laid  in  clay,  and  the  face  of  such  a  brick  stopping  may 
be  plastered  with  clay  to  prevent  any  leakage  of  air  or  gas. 
Such  a  stopping  is  called  a  sealed  stopping,  and  the  opening 
that  it  closes  is  said  to  be  sealed  or  sealed  off.  Board  stop- 
pings are  sometimes  used  for  temporary  purposes. 

8.  Air  Crossings,  Air  Bridges,  Overcasts,  Under- 
casts. — Any  form  of  construction  by  which  one  air-current 
is  made  to  pass  over  or  under  another  air-current  is  called 


FIG.  6 

an  air  crossing;  air  crossings  are  called  overcasts  when 
they  pass  over  another  airway,  Figs.  6  and  7,  and  under- 
casts  when  they  pass  under  another  airway,  Fig.  8.  An  air 
crossing,  Fig.  6,  may  be  driven  entirely  in  the  roof  strata 
and  some  distance  above  the  other  airway;  in  this  form  of 
crossing  there  is  no  connection  between  the  two  airways  at 
the  point  where  they  cross  each  other.  A  more  common 
form  of  air  crossing,  called  an  all*  bridge,  is  shown  in 
Fig.  7.  An  undercast  is  shown  in  Fig.  8.  The  relative 
advantages  and  disadvantages  of  these  different  kinds  of 
air  crossings  are  as  follows: 

An  overcast  driven  entirely  in  the  rock  is  often  more 
expensive  to  build  than  the  common  form  of  air  bridge,  but 
it  is  perfectly  air-tight  and  there  is  no  loss  of  air  by  leakage. 
It  is  often  stated  as  an  advantage  that  such  an  overcast 


8  MINE  VENTILATION  §13 

cannot  be  destroyed  by  the  force  of  a  mine  explosion,  but  the 
conditions  in  a  mine  in  this  respect  are  so  numerous  that  the 
destruction  of  an  overcast  may  or  may  not  prove  a  disad- 
vantage. If  the  force  of  the  explosion  finds  relief  by  blowing 
down  an  air  bridge,  this  may  prevent  the  extension  of  the 
explosion  into  another  section  of  the  mine,  owing  to  the 


immediate  expansion  and  cooling  of  the  gases  in  the  mine. 
On  the  other  hand,  if  there  is  not  a  way  of  escape  for  men 
from  other  portions  of  the  mine,  the  destruction  of  an  air 


FIG.  8 

bridge  may  spread  the  afterdamp  to  parts  of  a  mine  to  which 
it  might  not  otherwise  have  gone.  Again,  if  an  air  bridge  is 
not  destroyed  by  an  explosion,  it  may  cause  the  air-current 
to  force  a  large  volume  of  poisonous  gases  into  sections 
of  the  mine  that  Otherwise  would  not  be  affected  by  the 
explosion.  For  these  reasons,  it  is  a  question  whether  tight 


§13  MINE  VENTILATION  9 

stoppings  or  loosely  built  stoppings  that  will  be  easily  blown 
out  by  an  explosion  are  the  better. 

An  undercast  constructed  as  shown  in  Fig.  8  has  the 
decided  disadvantage  that  a  basin  is  formed  in  which  water 
or  gas  may  collect.  Any  accumulation  of  water  under  the  air 
bridge  reduces  the  sectional  area  of  the  air  passage,  and  may 
completely  close  the  airway.  In  case  of  emergency,  the 
undercast  may  be  found  impassible  and  perhaps  the  only 
means  of  escape  thereby  cut  off.  The  common  form  of  air 
bridge  shown  in  Fig.  7  is  constructed  by  blowing  down  the 
roof  in  the  cross-entry  on  each  side  of  the  haulage  road  or 
air-course,  and  driving  a  passage  up  through  the  roof  strata 
overlying  the  haulage  road.  When  this  has  been  done  and 
the  rock  dressed,  strong  timber  frames  a  are  constructed  on 
each  side  of  the  haulage  road  and  heavy  cross-beams  b  are 
laid  over  these  in  line  with  the  air  crossing;  rails  are  some- 
times used  for  this  purpose.  A  double  thickness  of  plank  c,  d 
laid  at  right  angles  to  each  other  or  so  as  to  break  joints  is 
then  laid  on  these  cross-beams  and  over  them  a  bed  of  sand 
or  clay.  The  joints  between  the  overcast  and  the  haulage 
road  are  then  carefully  sealed  with  clay  or  other  luting 
material,  so  that  no  air  can  leak  from  the  overcast  into  the 
roadway.  Timber  is  then  set  to  secure  the  roof  of  the  over- 
cast, either  as  shown  in  the  figure  or  as  called  for  by  the 
local  conditions. 

The  construction  of  overcasts,  mine  doors,  brattices,  and 
stoppings  is  often  regulated  by  law  and  must  in  some  states 
be  approved  by  the  mine  inspector  for  the  district. 


FORM    AND    SIZE    OF    AIRWAYS 

9.  The  five  forms  of  airways  more  or  less  commonly 
used  in  mines  are  shown  in  Fig.  9;  these  are  the  circular  (a), 
square  (b} ,  rectangular  (<:),  arched  (d),  and  trapezoidal  (<?). 
The  perimeter  of  an  airway  is  the  polygon  or  curve  bound- 
ing a  cross-section  of  an  airway.  The  perimeter  of  a  cir- 
cular airway  is  its  circumference.  The  perimeter  of  a  square 
airway  is  four  times  the  length  of  one  of  its  sides.  The 


10 


MINE  VENTILATION 


§13 


perimeter  of  a  rectangular  airway  is  the  sum  of  the  length 
of  the  four  sides  of  the  airway,  and  may  be  found  by  adding 
the  height  of  the  airway  to  its  width  and  multiplying  their 
sum  by  two.  The  perimeter  of  the  arched  airway  i£  the  sum 
of  the  lengths  of  the  three  straight  sides  and  the  curve. 
The  perimeter  of  the  trapezoidal  airway  is  the  sum  of  the 
lengths  of  the  four  sides. 

The  sectional  area  of  an  airway,  often  referred  to  simply 
as  the  area,  is  the  area  of  a  cross-section  of  the  airway. 
This  area  is  designated  a  in  ventilation  formulas.  The  area 
of  a  circular  airway  is  equal  to  the  area  of  a  circle  whose 


FIG.  9 

diameter  is  the  diameter  of  the  airway.  The  area  of  a 
square  airway  is  equal  to  the  square  of  one  side  of  the  air- 
way. The  area  of  a  rectangular  airway  is  the  product  of 
the  height  and  width  of  the  airway.  These  dimensions'  are 
found  by  carefully  measuring  the  height  of  the  airway  where 
the  observation  is  taken  and  the  average  width,  making 
allowance,  as  the  judgment  may  dictate,  for  unavoidable 
timbers.  The  area  of  a  trapezoidal  airway  equals  the  prod- 
uct of  the  height  by  one-half  the  sum  of  the  top  and  bot- 
tom widths.  The  area  of  an  arched  airway  is  found  by 
separately  calculating  the  area  of  the  lower  cross-section 
bounded  by  straight  lines,  and  that  of  the  upper  section 


§13  MINE  VENTILATION  11 

bounded  by  the  roof  curve  and  the  top  line  of  thj  lower  sec- 
tion, and  adding  these  two  areas  together. 

The  rubbing  surface  of  an  airway  is  the  entire  inner 
surface  of  the  airway  composed  of  the  roof,  floor,  and  sides. 
It  is  estimated  in  square  feet  and  is  found  by  multiplying 
the  perimeter  of  the  airway  by  its  length.  Expressed  as  a 
formula,  this  is 

s  =  lo 
in  which      s  =  rubbing  surface  of  airway,  in  square  feet; 

/  =  length  af  airway,  in  feet; 

o  =  perimeter  of  airway,  in  feet. 

EXAMPLE. — Find  the  perimeter,  rubbing  surface,  and  area  of  an 
airway  6  ft.  X  10  ft.  and  1,000  feet  long. 

SOLUTION.— The  perimeter  is  2  (6  +  10)  =  32  ft.     Ans. 
The  rubbing  surface  is  32  X  1,000  =  32,000  sq.  ft.     Ans. 
The  area  is  6  X  10  =  60  sq.  ft.     Ans. 


10.  Comparison  of  Forms  of  Airways. — The  resist- 
ance offered  to  the  passage  of  an  air-current  through  an  airway 
depends  on  the  amount  and  character  of  the  rubbing  surface; 
and  since  air-ways  having  the  same  area  of  cross-section  may 
have  different  perimeters,  it  is  advisable,  if  practicable,  to 
choose  that  form  of  airway  that  has  the  smallest  perimeter 
for  a  given  sectional  area.  For  the  same  amount  of  rubbing 
surface  and  the  same  perimeter,  the  larger  the  sectional  area, 
the  greater  will  be  the  quantity  of  air  in  circulation.  As  the 
circular  airway  presents  the  smallest  perimeter  or  rubbing 
surface  for  a  given  area,  it  will  offer  the  least  resistance  to 
the  passage  of  the  air  and  will  pass  the  largest  quantity  of 
air  with  the  least  expenditure  of  power. 

Practical  considerations,  however,  determine  to  a  great 
extent  the  form  of  airway  to  be  adopted  in  any  particular 
case.  The  circular  is  not  a  practical  form  for  an  airway, 
since  it  furnishes  no  roadbed,  the  shape  is  difficult  to  main- 
tain in  driving,  and  in  stratified  material  the  sides  and  top  of 
this  form  are  difficult  to  support.  The  height  of  the  airway 
is  generally  determined  by  the  height  of  the  seam,  except  in 
thick  seams,  and  the  nearer  a  rectangular  airway  approaches 
to  a  square  airway,  the  more  air  it  will  pass. 


12 


MINE  VENTILATION 


§13 


Table  I  shows  that  for  a  given  sectional  area  the  circular 
airway  has  less  rubbing  surface  than  a  square  airway,  and 
the  square  airway  less  rubbing  surface  than  a  rectangular 
airway.  That  form  of  rectangular  airway  which  most  nearly 
approaches  the  square  form  has  the  less  rubbing  surface. 
The  arched  airway,  which  combines  the  circular  and  the 
square  or  rectangular  form  is  better  in  this  respect  than 
the  square  or  rectangular  form  alone.  Since  circular  airways 
are  seldom  practicable,  arched  or  square  airways  should  be 
used  whenever  possible,  and  if  rectangular  or  trapezoidal 
TABLE  I 


Form  of 

Dimensions  of 

Length 

Perim- 

Rubbing 
Surface 

<rt  ^ 
l| 

Section 

Section 

Feet 

Feet 

Square 
Feet 

n  | 
o  cr 

Circular  '.    . 

9.026'  diam. 

I,OOO 

28.36 

28,360 

64 

Arched     .    .  j 

8'  wide  X  8.86  high 

1,000 

30.29 

30,290 

64 

Square     .    . 

8'X  8' 

1,000 

32.00 

32,000 

64 

Trapezoidal 

(io'and6')x8.25' 

1,000 

32.50 

32,500 

64 

Rectangular 

10.666'  X  6' 

1,000 

33-33 

33,333 

64 

Rectangular 

16'  X  4' 

1,000 

40.00 

40,000 

64 

airways  are  absolutely  necessary,  they  should,  in  so  far  as  is 
practicable,  approach  the  square  form. 


EXAMPLES    FOR    PRACTICE 

1.  Find  the  perimeter,  rubbing  surface,  and  sectional  area  of  an 
airway  9  ft.  X  12  ft.  and  2,000  feet  long. 

(Perimeter,  42  ft. 
Rubbing  surface,  84,000  sq.  ft. 
Sectional  area,  108  sq.  ft. 

2.  Find  the  sectional  area  of  an  airway  that  measures  6  feet  in 
Width  at  the  top,  10  feet  in  width  at  the  bottom,  and  is  8  feet  high. 

Ans.  64  sq.  ft. 


§13  MINE  VENTILATION  13 

3.  Find  the  perimeter,  rubbing  surface,  and  sectional  area  of  a  cir- 
cular airway  9  feet  in  diameter  and  1,000  feet  long. 

(Perimeter,  28.27  ft. 
Rubbing  surface,  28,274  sq.  ft. 
Sectional  area,  63.6  sq.  ft. 

4.  Find  the  perimeter,  rubbing  surface,  and  sectional  area  of  an 
arched  airway  10  feet  wide    10  feet  high  to  the  crown  of  the  arch,  and 
LOGO  feet  long. 

f  Peri  meter,  35.7  ft. 
Ans.{  Rubbing  surface,  35,708  sq.  ft. 
I  Sectional  area,  89.27  sq.  ft. 

5.  What  is  the  total  rubbing  surface  in  a  circular  shaft  15  feet  in 
diameter  and  1,200  feet  deep  divided  into  two  equal  compartments  by  a 
partition,  the  thickness  of  which  may  be  neglected?     Ans.  92,549  sq.ft. 


11.  Similar  Airways. — Two  airways  are  similar  when 
their   cross-sections    are    similar  figures.     Two  figures  are 
similar  when  their  corresponding 

angles  are  equal  and  their  corre- 
sponding sides  proportional. 
Circles  and  squares  are  always 
similar.  When  the  smaller  of 
two  similar  rectangles  or  trape- 
zoids  is  placed  within  the  larger,  FlG- 10 

so  that  any  two  corresponding  sides  are  parallel,  the  two  other 
corresponding  sides  will  also  be  parallel,  each  to  each.  Fig.  10 
shows  two  similar  trapezoids  so  placed  that  their  correspond- 
ing sides  are  parallel.  Many  of  the  problems  in  mine  venti- 
lation are  considerably  shortened  by  the  application  of  special 
rules  or  formulas,  when  it  is  known  that  they  relate  to  similar 
airways. 

HOW    AIR-CURRENTS    ARE    PRODUCED 

12.  fluids  always  move  from  a  point  of  higher  pressure 
toward  a  point  of  lower  pressure;  the  moving  force  is  the  dif- 
ference between  the  two  pressures,  and  it  is  on  this  principle 
that  the  production  of  an  air-current  depends.    No  air-current 
is  produced  in  an  airway  when  the  pressure  is  the  same  at 
both  ends  of  the  airway;  but  if  by  some  means  the  pressure 
at  either  end  is  increased  or  decreased  with  respect  to  that  at 


14  MINE  VENTILATION  §13 

the  other  end,  a  current  of  air  is  at  once  produced  in  the  air- 
way, its  direction  being  from  the  greater  toward  the  lesser 
pressure.  The  end  where  the  air  enters  the  airway  is  called 
the  intake  end,  or  simply  the  intake,  and  that  where  the  air  is 
discharged  into  the  atmosphere  the  return  end,  or  the  return, 
of  the  airway.  The  pressure  at  the  intake  end  is  always 
greater  than  that  at  the  return  end  of  the  airway  or  the  air 
would  not  flow,  and  the  difference  between  these  pressures  is 
called  the  ventilating  pressure,  as  it  is  this  difference  in 
pressure  that  causes  the  circulation  of  air  through  the  airway. 

The  unit  of  ventilating  pressure  is  the  amount  by  which  the 
intake  pressure  exceeds  the  return  pressure  expressed  in 
pounds  per  square  foot. 

The  ventilating  pressure  is  given  by  the  following  formula: 

P=  pa 
in  which,  P  =  ventilating  pressure,  in  pounds; 

P  =  unit  of  ventilating  pressure,  in   pounds  per 

square  foot; 
a  =  sectional  area  of  airway,  in  square  feet. 

The  pressure  creating  an  air-current  is  well  illustrated  by 
the  difficulty  experienced  in  opening  a  door  in  a  mine 
against  the  air-current.  For  example,  if  a  mine  door  is 
5  feet  high  and  6  feet  wide  and  the  unit  of  ventilating  pres- 
sure is  10  pounds  per  square  foot,  the  total  pressure  against 
the  door  is  5  X  6  X  10  =  300  pounds;  and  this  must  be  over- 
come before  the  door  can  be  opened. 

13.  A  circulation  of  air  through  a  mine  airway  may  be 
produced  by  natural  or  artificial  means.  Natural  ventilation 
includes  all  circulations  of  air  caused  by  the  natural  heat  of 
the  mine  in  a  shaft  or  slope  or  in  rise  or  dip  workings. 
Artificial  ventilation  is  produced  by  such  means  as  the 
waterfall,  wind  cowl,  furnaces,  steam  jets,  and  all  forms  of  air 
pumps  and  fans.  All  these  means  for  producing  a  circulation 
of  air  in  a  mine  or  airway  act  by  creating  a  difference  of 
pressure  between  the  intake  and  the  return  openings  of  the 
airway.  The  action  of  each  of  these  means  of  producing 
ventilation  will  be  described  later. 


§18 


MINE  VENTILATION 


15 


14.  Systems  of  Ventilation. — There  are  two  general 
systems  of  mine  ventilation,  known  as  the  blowing,  or 
plenum,  system,  and  the  exhaust,  or  vacuum,  system.  In  the 
blowing  system,  as  shown  in  Fig.  11,  the  pressure  on  the 
air  in  the  mine,  known 


as  the  mine  pressure^ 
is  always  above  the 
atmospheric  pres- 
sure, while  in  the 
exhaust  system, 
Fig.  12,  the  mine  pres- 
sure is  below  the  atmospheric  pressure.  In  a  blowing  sys- 
tem, the  means  of  ventilation  is  placed  at  the  intake  end  of 
the  airway  and  increases  the  pressure  at  that  point  above 
the  atmospheric  pressure.  This  increase  of  pressure  is  the 
ventilating  pressure.  In  the  exhaust  system,  the  means  of 
ventilation  is  placed  at  the  return  end  of  the  airway  and 


PIG-U 


FIG.  12 

reduces  the  pressure  at  that  point  below  the  atmospheric 
pressure;  the  decrease  in  this  case  is  the  ventilating  pres- 
sure. In  the  blowing  system,  as  the  mine  pressure  is  greater 
than  the  atmospheric  pressure,  every  crack  or  crevice  in  the 
surface  furnishes  a  way  of  escape  for  the  mine  air  and  gases. 
In  the  exhaust  system,  on  the  other  hand,  as  the  mine  pres- 
sure is  less  than  the  atmospheric  pressure,  every  crack  and 
crevice  in  the  surface  furnishes  a  way  for  the  atmospheric 
air  to  enter  the  mine.  In  the  first  case,  the  pressure  acts 
from  the  mine  into  the  atmosphere;  in  the  second  case,  it  is 
from  the  atmosphere  into  the  mine. 


16  MINE  VENTILATION  §13 

GENERAL   PRINCIPLES    OF   VENTILATION 

15.  Factors  of  a  Circulation  of  Air. — Briefly  stated, 
the  general  principles  underlying  the  subject  of  mine  ventila- 
tion are  as  follows:  In  every  circulation  of  an  aip-current, 
Power  is  used  in  overcoming  the  resistance  of  the  airway,  and 
in  doing  this,  a  certain  velocity  and  pressure  are  produced  and  a 
certain  quantity  of  air  is  circulated,  thereby  accomplish- 
ing a  certain  amount  of  work. 

The  factors  concerned  in  the  circulation  of  air  in  an  airway 
may  be  grouped  in  the  following  three  classes: 

Producing  Factors — the  power  producing  the  circulation; 

Resisting  Factors — the  total  rubbing  surface  and  the  unit 
of  resistance.  Then,  the  unit  of  resistance  is  the  resistance 
offered  to  the  passage  of  an  air-current  by  a  unit  area  of 
rubbing  surface  for  a  velocity  of  1  foot  per  minute; 

Resulting  Factors — the  velocity,  quantity,  and  pressure  of 
the  air,  and  the  work  accomplished  in  moving  a  certain  quan- 
tity of  air  at  a  given  velocity  and  pressure. 

When  an  air-current  passes  through  an  airway  as  the  result 
of  a  certain  ventilating  pressure  having  been  applied  to  the 
air,  it  is  opposed  by  a  certain  resistance  developed  in  the  air 
way  due  to  the  rubbing  surface.  Three  conditions  may  be 
presented  as  follows: 

1.  If  an  airway  has  the  ends  closed,  the  power  applied 
produces  pressure,  but  no  velocity  and  consequently  no  flow 
of  air  or  no  quantity;  this  is  called  the  static  condition,  and 
is  only  considered  in  special  cases  in  mine  practice. 

2.  If  an  airway  consists  of  an  opening  in  a  thin  plate 
so  that  it  has  practically  no  length,  the  power  applied  pro- 
duces  velocity  and  quantity  but   no  pressure;    this  is  the 
theoretical  condition  and  does  not  represent  any  condition 
existing  in  a  mine  and  its  only  use  is  in  certain  theoretical 
calculations. 

3.  In  an  airway  with  the  ends  open  and  of  some  length, 
the  power  applied  produces  pressure,  velocity,  and  quantity; 
this  is  the  normal  working  condition  of  a  mine  as  presented 
in  the  general  practice  of  mine  ventilation. 


§13  MINE  VENTILATION  17 

16.  Quantity  of  Air  In   Circulation. — The  quantity* 
of  air  passing  through  an  airway  is  found  by  multiplying  the 
sectional  area  of  the  airway  by  the  velocity  of  the  air-current, 
as  expressed  by  the  formula 

q  =  av 
in  which  q  =  quantity  of  air  in  circulation,  in  cubic  feet  per 

minute; 

a  =  sectional  area  of  airway,  in  square  feet; 
,  v  =  velocity  of  air-current,  in  feet  per  minute. 

The  quantity  of  air  passing  through  a  given  section  of  air- 
way, therefore,  depends  on  the  velocity  of  the  air-current,  and 
anything  that  affects  the  velocity  will  affect  the,  quantity  in 
the  same  proportion. 

EXAMPLE. — Calculate  the  quantity  of  air  passing  in  an  airway  8  ft. 
X  10  ft.,  when  the  velocity  of  the  air-current  is  600  feet  per  minute. 

SOLUTION. — Substituting  the  given  values  in  the  formula,  the 
quantity  of  air  in  circulation  is 

q  =  8  X  10  X  600  =  48,000  cu.  ft.  per  min.     Ans. 

The  velocity  of  the  air-current  is  the  rate  of  travel  of 
the  air  in  the  airway  expressed,  generally,  in  feet  per  minute. 
The  quantity  of  air  passing  out  of  the  mine  by  the  return  air- 
way is  almost  always  greater  than  the  quantity  of  air  passing 
into  the  mine  by  the  intake  airway  for  several  reasons;  there 
is  always  some  gas  given  off  in  the  mine  workings,  and  the 
volume  of  this  gas  goes  to  increase  the  volume  of  the  return 
current;  the  return  current  is  generally  warmer  than  the  intake 
and  the  air  is  thereby  expanded  and  its  volume  increased; 
and  as  the  pressure  on  the  return  air-current  is  always  less 
than  that  on  the  intake  there  is  a  slight  increase  in  the  vol- 
ume of  the  return  current  due  to  this  cause.  In  speaking  of 
the  amount  of  air  circulating  in  a  mine,  the  quantity  of  air 
passing  on  the  main  intake  airway  is  referred  to  and  not  that 
on  the  return.  

MINE    RESISTANCE 

17.  Definition. — Every  airway  offers  a  certain  resist- 
ance to  the  passage  of  an  air-current  by  virtue  of  its  rubbing 
surface  and  its  sectional  area.     The  resistance  of  the  airway 
is  caused  by  the  rubbing  of  the  air-current  on  the  sides,  top, 


18  MINE  VENTILATION  §13 

and  bottom  of  the  airway;  it  is  frictional  resistance.  The 
amount  of  resistance  offered  depends  on  the  amount  of  the 
rubbing  surface  and  on  the  velocity  of  the  air-current,  and 
this  depends  on  the  power  applied.  The  application  of  a 
certain  power  to  an  airway  will  produce  a  velocity  v,  which 
will  be  greater  or  less  according  to  the  resisting  power  of 
the  airway.  For  the  same  power  applied,  the  greater  the 
resisting  power  of  the  airway,  the  less  will  be  the  velocity 
produced;  and  the  less  the  resisting  power  of  the  airway,  the 
greater  will  be  the  velocity  produced.  This  will  be  more 
clearly  understood  by  the  following  illustration:  Suppose 
that  a  small  blower  is  attached  to  one  end  of  a  long  garden 
hose;  it  is  possible  to  increase  the  length  of  the  hose  so  that 
with  the  greatest  force  or  pressure  that  can  be  produced  by 
the  blower  there  is  very  little  flow  of  air  through  the  hose 
owing  to  the  great  resistance  due  to  its  length  and  rubbing 
surface.  A  pressure  gauge  attached  to  the  hose  near  the 
blower  will  show  a  high  pressure,  while  the  velocity  of  the 
air  in  the  hose  is  very  small.  If,  now,  the  hose  is  cut  off  a 
short  distance  from  the  blower,  the  conditions  with  respect 
to  velocity  and  pressure  are  at  once  reversed,  there  is  a  large 
quantity  of  air  flowing  through  the  short  length  of  hose,  and 
the  pressure  as  shown  by  the  gauge  has  dropped  to  a  small 
amount.  This  illustration  also  shows  that  the  pressure  of 
the  air,  and  consequently  the  resistance  of  the  airway,  is  due 
to  the  resisting  power  of  the  airway  as  determined  by  its 
length  and  size,  and  to  the  ventilator  producing  the  current. 
While  every  airway  has  a  certain  resisting  power  depend- 
ent on  its  rubbing  surface  and  area,  there  is  no  resistance 
developed  in  any  case  until  a  current  has  been  established. 

18.  The  value  of  an  airway  for  purposes  of  ventilation 
is  determined  by  its  capacity  for  passing  the  largest  quantity 
of  air  with  the  least  expenditure  of  power.  In  general,  the 
larger  the  area  of  an  airway  the  greater  is  its  capacity  for 
passing  air;  but,  on  the  other  hand,  the  greater  its  resisting 
power,  the  smaller  is  the  quantity  of  air  for  the  same  power 
producing  the  current. 


§13  MINE  VENTILATION  19 

The  resisting  power  of  an  airway,  which  reduces  its  capac- 
ity for  passing  air  by  reducing  the  velocity  at  which  the  air 
flows,  is  equal  to  the  product  of  the  unit  resistance  k  by 
the  amount  of  rubbing  'surface  s.  The  unit  of  resistance, 
generally  called  the  coefficient  of  friction,  is  the  resistance, 
in  pounds,  offered  by  1  square  foot  of  rubbing  surface  to  an 
air-current  having  a  velocity  of  1  foot  per  minute.  Multiply- 
ing the  unit  of  resistance  by  the  rubbing  surface  of  an  airway 
gives  the  resistance  k  s  of  that  airway  for  a  velocity  of  1  foot 
per  minute.  As  the  velocity  of  the  air-current  increases,  the 
same  volume  of  air  strikes  a  larger  extent  of  rubbing  surface 
in  the  same  time  and  with  a  greater  force.  If  the  velocity  be 
doubled,  each  particle  of  air  rubbing  against  the  rubbing  sur- 
face meets  twice  the  number  of  resisting  particles  as  before, 
and  strikes  each  particle  with  a  blow  twice  as  hard,  making 
the  resistance  in  this  case  2x2  =  4  times  as  great  as  before. 
If  the  velocity  is  increased  to  three  times  the  original  veloc- 
ity, each  particle  of  air  meets  with  three  times  the  number  of 
resisting  particles  and  strikes  each  particle  with  a  blow  three 
times  as  hard  as  when  moving  at  the  original  velocity, 
making  the  total  resistance  in  this  case  3x3  =  9  times  the 
original  resistance;  thus  the  resistance  is  seen  to  increase  as 
the  square  of  the  velocity.  Therefore,  the  resistance  of  an 
airway  is  given  by  the  formula 

R  =  ksv* 
in  which        R  =  resistance  of  airway,  in  pounds; 

k  =  unit  of  resistance  in  pounds  .00000002; 

s  =  rubbing  surface,  in  square  feet; 

v  =  velocity  of  air,  in  feet  per  minute. 

19.  Value  of  Unit  of  Resistance,  or  Coefficient  of 
Friction,  k. — The  unit  of  resistance,  commonly  called  the 
coefficient  of  friction,  varies  with  the  nature  of  the  rub- 
bing surface,  but  is  practically  a  constant  for  any  given  class 
or  type  of  mines.  Numerous  values,  shown  in  Table  II,  have 
been  given  by  different  authorities  for  the  coefficient  of 
friction,  many  of  which  perhaps  apply  to  different  classes  of 
mines. 


20  MINE  VENTILATION  §13 

In  American  practice,  the  Atkinson  and  Fairley  coefficients 
have  been  mostly  used.  The  Atkinson  coefficient,  which  is 
more  than  twice  as  great  as  the  Fairley  coefficient,  has  been 
found,  however,  to  give  practical  results  in  seams  from  4  feet 
to  6  feet  in  thickness.  If  this  coefficient  is  too  high,  it  errs 
on  the  safe  side,  since  it  is  always  advisable  to  have  plenty 
of  air  throughout  a  mine.  The  method  of  mining,  mode  of 
timbering,  and  other  details  of  working,  as  well  as  the  thick- 
ness of  the  seam,  all  of  which  vary  considerably  in  different 
localities,  determine  practically  the  coefficient  of  friction  best 

TABLE  II 


Values  of  k 

J.  J.  Atkinson 

.00000002  i  7 

W.  Fairley     

.00000001 

G.  G.  Andre 

000000022424 

Peclet  

.000000003697 

D'Aubuisson 

000000001955 

Navier             

.00000000  i  872 

J.  Stanley  James  
D.  Murgue 

.00000000929 
.000000008242 

adapted  to  such  local  conditions  or  types  of  mines.  The  value 
of  the  coefficient  of  friction  should,  therefore,  be  regarded 
as  representing  a  particular  class  of  mines. 

Owing  to  the  wide  difference  in  the  values  given  by  dif- 
ferent authorities  for  the  coefficient  of  friction,  and  further, 
owing  to  the  fact  that  it  is  possible  to  determine  this  value 
only  approximately,  and  because  such  value  is  often  applied 
indiscriminately  to  all  types  of  mines,  the  Atkinson  coeffi- 
cient will  be  abbreviated  and  the  value  k  =  .OOOOOOO2  will 
be  used  in  all  the  calculations  and  examples  following. 

20.     Calculation  of  the  Resistance  of  an  Airway. 

Since  the  ventilating  pressure,  P  =  pa,  which  is  the  total 
pressure  exerted  on  the  sectional  area  of  the  airway,  over- 
comes the  resistance  of  the  airway  when  the  current  is 


§13 


MINE  VENTILATION 


21 


established  and  the  velocity  of  the  air  is  uniform,  the  venti- 
lating pressure  is  equal  to  the  resistance  R  of  the  airway  to 
the  air-current.  R  =  ksv*.  Then,  since  P  =  R, 

R=pa  (1) 

and  R  =  ksv*  (2) 

pa  =  ksv*  (3) 

Since  the  unit  resistance  is  given  in  pounds,  the  total 
resistance  will  also  be  in  pounds. 

The  resistance  of  an  airway  to  the  passage  of  an  air-cur- 
rent depends  therefore  on  three  elements — the  unit  resistance, 
the  rubbing  surface,  and  the  velocity  of  the  air-current. 
Opposed  to  the  mine  resistance  R  is  the  ventilating  pres- 
sure P  =  pa. 

EXAMPLE:. — Find  the  resistance  of  an  airway  8  ft.  X  10  ft.  and 
2,500  ft.  long,  when  the  velocity  of  the  air-current  is  600  feet  per 
minute. 

SOLUTION. — The  perimeter  of  this  airway  o  =  2(8  +  10)  =  36  ft.,  and 
the   rubbing   surface   is   s  =  lo  =  2,500X36  =  90,000  sq.  ft.     If  k 
=  .00000002,  substituting  the  given  values  in  formula  2, 
R  =  .00000002  X  90,000  X  600'  =  648  Ib.     Ans. 

21.  Illustration. — Fig.  13  illustrates  the  manner  in 
which  the  mine  resistance  or 
the  resistance  of  an  airway 
opposes  the  ventilating  pres- 
sure of  the  air.  The  cross- 
section  xy  of  an  airway  is 
represented  as  a  piston.  The 
small  arrows  on  the  left  of  xy 
represent  the  units  of  ventila- 
ting pressure  acting  on  each 
square  foot  of  the  sectional 
area,  giving  a  total  pressure  pa 
acting  in  the  direction  of  the 
small  arrows.  The  total  pressure  pa  may  be  supposed  to 
move  against  the  resistance  R  of  the  airway  in  the  same 
manner  as  it  would  move  in  raising  a  weight  W  equal  to  R. 
The  vertical  height  through  which  this  weight  is  raised  in 


Airway 


FIG. 13 


22  MINE  VENTILATION  §13 

1  minute  is  equal  to  the  velocity  of  the  air-current  v  expressed 
in  feet  per  minute.  Since  the  resistance  of  an  airway  is  equal 
to  the  total  pressure^*  a  exerted  on  the  sectional  area  of  such 
airway,  the  unit  of  ventilating  pressure  />,  or  the  pressure 
per  square  foot  of  area,  is  equal  to  the  resistance  of  the  air- 
way divided  by  the  sectional  area,  that  is, 


22.     Calculation  of  Unit  of  Ventilating  Pressure. 

Since  the  resistance  of  an  airway  ksv*  is  equal  to  the  ven- 
tilating pressure  pa,  the  unit  of  ventilating  pressure  /  in  any 
circulation  is  always  equal  to  the  resistance  of  the  airway 
divided  by  its  sectional  area,  as  expressed  by  the  formula 


EXAMPLE.  —  Find  the  unit  of  ventilating  pressure  in  an  airway 
8  ft.  X  10  ft.  and  2,500  feet  long,  when  the  velocity  of  the  air-current 
is  600  feet  per  minute. 

SOLUTION.  —  The  resistance  of  this  airway  was  found  in  the  example 
in  Art.  2O  to  be,  k  s  v*  =  648  Ib.  The  sectional  area  of  the  airway  is 

a  =  8X  10  =  80  sq.ft.;  then,^  =  ^~-  =  ~  =  ^  =  8.1  Ib.  per  sq.  ft. 

Or,  substituting  the  given  values  in  the  above  formula, 
=  .00000002X90.000X600:  =  ^ 

o(J 


POWER    AND    WORK    IN    PRODUCING    AN    AIR-CURRENT 

23.  Work. — Whenever  a  force  acts  through  a  given  dis- 
tance, -work  is  performed,  and  the  quantity  of  work  is  then 
measured  by  the  product  of  the  force,  in  pounds,  and  the 
distance  through  which  it  acts,  in  feet.  That  is,  suppose 
that  it  takes  a  force  (pressure)  of  25  pounds  to  move  a  cer- 
tain body;  then,  if  the  resistance  is  uniform,  as,  for  example, 
in  lifting  a  weight,  and  the  body  is  moved  through  a  dis- 
tance of  36  feet,  the  work  done  is  25  X  36  =  900  foot-pounds. 
Work  may,  therefore,  be  expressed  in  foot-pounds,  and 
represents  a  given  weight  (pounds)  raised  through  a  vertical 
height  (feet),  or  a  given  pressure  (pounds),  exerted  through 


§13  MINE  VENTILATION  23 

a  given  distance  (feet).  Work  is  independent  of  the  time 
in  which  it  is  performed;  that  is,  in  the  case  just  cited,  no 
matter  whether  it  takes  1  second  or  1  year  to  move  the 
body  36  feet,  the  work  done  is  900  foot-pounds. 

24.  Calculation  of  Work.—  When  the  velocity  of  the 
air-current  is  expressed  in  feet  per  minute,  the  work  per- 
formed each  minute  is  equal  to  the  product  of  the  total 
maving  pressure,  or  the  ventilating  pressure,  p  a  and  the 
velocity  v  of  the  air-current;  or,  since  the  ventilating  pres- 
sure is  equal  to  the  mine  resistance  fcsv*,  the  work  performed 
each  minute  may  be  found  by  multiplying  the  mine  resistance 
by  the  velocity  of  the  air-current,  giving  the  formulas, 

u  =  pa  v  (1) 

and  u  =  ksv*          (2) 

Since  the  distance  through  which  the  pressure  moves  in 
ventilation  is  expressed  as  velocity  in  feet  per  minute,  the 
work  performed  each  minute  is  equal  to  the  power  on  the 
air.  The  work  performed  in  the  circulation  of  air  in  an  air- 
way is  illustrated  in  Fig.  13,  the  vertical  height  through 
which  the  weight  is  raised  in  1  minute  being  equal  to  the 
velocity  af  the  air-current  expressed  in  feet  per  minute. 

EXAMPLE  1.  —  Find  the  power  on  the  air,  in  an  airway  8  ft.  X  10ft., 
when  the  velocity  of  the  air-current  is  600  feet  per  minute,  and  the  unit 
of  ventilating  pressure  is  8.1  pounds  per  square  foot. 

SOLUTION.—  The  area  a  is  8  X  10  =  80  sq.  ft.;  then,  substituting 
the  given  values  in  formula  1,  the  power  on  the  air  is 

^=^0^  =  8.1X80X600  =  388,800  ft.-lb.  per  minute. 
The  horsepower  of  this  circulation  is 


EXAMPLE  2.  —  Calculate  the  power  on  the  air  required  to  produce  a 
velocity  of  600  feet  per  minute  in  an  airway  8  ft.  X  10  ft.  and  2,500  feet 
long. 

SOLUTION.—  The  rubbing  surface  s  =  2(8  +  10)  X  2,500  =  90,000sq. 
ft.;  substituting  the  given  values  in  formula  2,  the  power  on  the  air  is 
u  =  ksv*  =  .00000002  X  90,000  X  600'  =  388,800  ft.-lb.  per  min. 

Ans. 


24  MINE  VENTILATION  §13 

This  example  can  also  be  worked  by  first  finding  the  resistance  of 
the  airway,  and  multiplying  this  resistance  by  the  velocity;  thus, 

R  =  k  s  v*  =  .00000002  X  90,000  X  600*  =  648  Ib. 
«  =  £5Z>'XZ'  =  648X600  =  388,800  ft.-lb.  per  minute.    Ans. 

Again,  since  the  quantity  of  air  in  circulation  q  is  equal  to 
the  sectional  area  a  multiplied  by  the  velocity  v,  by  substi- 
tuting q  for  av  in  formula  1, 

u  =  pav  =  Pq  (3) 

EXAMPLE  3. — Find  the  power  on  the  air  when  the  quantity  in  cir- 
culation is  48,000  cubic  feet  per  minute,  and  the  unit  of  ventilating 
pressure  is  8.1  pounds  per  square  foot. 

SOLUTION. — Substituting  the  given  values  in  formula  3,  the  power 
on  the  air  is 

«  =  48,000  X  8.1  =  388,800  ft.-lb.  per  min.    Ans. 

The  three  formulas  given  in  this  article  show  that  the 
work  performed  each  minute  or  the  power  on  the  air  in  any 
circulation  is  equal  to  the  ventilating  pressure  pa,  or  the 
resistance  of  the  airway  ksv*,  multiplied  by  the  velocity  of 
the  air  v;  also  to  the  quantity  of  air  in  circulation  q  multi- 
plied by  the  unit  of  ventilating  pressure  p. 

25.  Power  on  the  Air. — Any  given  work  can  be  per- 
formed in  a  greater  or  less  time,  according  to  the  power 
applied;  thus,  if  two  men  have  twice  the  power  of  one  man, 
they  will  perform  twice  the  work  of  one  man  in  a  given  time. 
On  the  other  hand,  one  man  will  perform  the  same  work  as 
two  men,  in  twice  the  time  of  the  two  men  working  together. 
The  term  power,  therefore,  relates  to  the  performance  of 
a  given  work  in  a  given  time.     In  order  to  compare  the 
work  done  by  different  machines,  time  must  be  considered. 
Hence,  the  amount  of  work  done  in  overcoming  a  resistance 
of  1  pound,  through  a  space  (distance)  of  1  foot  in  1  minute 
(foot-pounds  per  minute),  is  called  the  unit  of  power  in 
ventilation.     The  power  on  the  air  is,  then,  the  number  of 
foot-pounds  of  work  performed  in  1  minute. 

26.  Horsepower. — To  estimate  the  power  of  machines 
and  to  avoid  the  use  of  high  numbers,  the  commonly  adopted 
unit  of  power  is  the  horsepower,  or  the  power  that  will 


§13  MINE  VENTILATION  25 

perform  33,000  foot-pounds  of  work  per  minute;  or,  in  other 
words,  the  power  necessary  to  raise  33,000  pounds  through 
a  vertical  height  of  1  foot  in  1  minute,  or  330  pounds  a  height 
of  100  feet,  or  33  pounds  a  height  of  1,000  feet,  in  the  same 
time.  Expressed  as  a  formula, 


33,000 

in  which  h  =  horsepower; 

*  u  =  units  of  power  (foot-pounds  per  minute). 


EXAMPLES    FOR    PRACTICE 

1.  (a)  Calculate   the   resistance   of   an    airway  6  ft.  X  8  ft.   and 
12,660  feet  long,  when  the  velocity  is  480  feet  per  minute,     (b)  Find 
the  unit  of  ventilating  pressure  in  this  circulation. 

A       f(a)  1,632+  lb. 

1S'\(£)  34+  lb.  per  sq.  ft. 

2.  (a)  Find  the   unit  of  ventilating  pressure  that  will   produce  a 
velocity  of  600  feet  per  minute  in  an  airway  6  ft.  X  8  ft.,  and  5,000  feet 
long,     (b)  What    quantity   of   air   is   in    circulation    in    this  airway? 
(c)  Find  the  power  on  the  air,  or  the  power  producing  this  circu- 
lation. f  (a)  21  lb.  per  sq.  ft. 

Ans.l  (b)  28,800  cu.  ft.  per  min. 
[(c)  604,800  ft.-lb.  per  rain. 

3.  (a)  What  work  will  be  performed  or  what  power  on  the  air  will 
produce  a  velocity  of  500  feet  per  minute  in  an  airway  8  feet  square 
and  3,000  feet  long?     (b)  What  is  the  horsepower  of  this  circulation? 

.        ((a)  240,000  ft.-lb.  per  min. 
ls-{(6)  9,454  H.  P. 

4.  What  work  will  be   performed  or  what  power  on  the  air  will 
circulate  60,000  cubic  feet  of  air  per  minute  against  a  pressure  of 
5.2  pounds  per  square  foot  and  what  horsepower  is  required  to  main- 
tain this  circulation?  .    e  f  312,000  ft.-lb.  per  min. 

Ans-\7,272  H.  P. 


AIR  MEASUREMENTS 


TO    MEASURE    THE    VELOCITY    OF    AIR    IN    AN    AIRWAY 

27.  Before  the  quantity  of  air  passing  in  an  airway  can 
be  calculated,  it  is  necessary  to  measure  the  velocity  of  the 
air-current.  For  this  purpose,  a  place  is  selected  in  the  air- 
way where  the  sectional  area  represents  a  fair  average  of 


MINE  VENTILATION 


§13 


the  whole  airway,  in  order  that  the  velocity  may  be  the 
average  velocity  of  the  air.  The  airway  should  also  be 
straight  and  free  from  any  obstruction  that  would  cause  the 
air-current  to  travel  on  one  side  of  the  airway  more  than  on 
the  other.  In  a  bend  of  the  airway  or  near  the  junction  of 
two  airways,  the  current  is  often  deflected  to  one  side  of  the 
passage,  especially  if  a  large  quantity  of  air  is  moving.  In 
such  cases,  it  is  not  easy  to  obtain  an  average  velocity  for  the 
airway.  The  velocity  of  the  air  is  measured  by  an  instru- 
ment called  the  anemometer. 

28.     The  Blram  anemometer,   Fig.  14,  consists  of  a 


number  of  small  arms  supported  on  a  light  axle  that  has 
almost  frictionless  bearings.  Blades  a  are  attached  to  these 
arms,  and  the  axle,  arms,  and  blades  constitute  what  is  called 
the  vane.  The  blades  of  the  vane  are  inclined  to  the  plane 


§13 


MINE  VENTILATION 


27 


of  revolution  and  are  given  such  a  pitch  that  one  revolution 
of  the  vane  corresponds  to  a  velocity  of  the  air-current  equal 
to  1  foot  per  minute.  At  the  center  of  the  instrument  is  a 
graduated  dial  for  registering  the  number  of  revolutions 
made  by  the  vane.  This  dial  contains  one  large  circle 
divided  into  one  hundred  equal  divisions;  each  of  these 
divisions  corresponds  to  one  revolution  of  the  vane,  so  that 
one  revolution  of  the  large  dial  hand,  or  pointer,  indicates 
one  hundred  revolutions  of  the  vane.  Within  the  large  circle 
of  the  dial,  there  are  five  small  circles,  each  provided  with  a 
separate  hand  or  pointer.  These  small  dials  are  marked 
C,  M,  X 'My  C  My  and  M,  indicating  that  they  register,  respect- 
ively, 100,  1,000,  10,000,  100,000,  and  1,000,000  .feet.  For 
example,  in  the  figure,  the  dials  XM,  CM,  and  M  all  read 
zero;  the  dial  M  reads 
two  divisions,  indica- 
ting 2,000  feet;  the 
dial  C  reads  one  divi- 
sion, indicating  100 
feet;  the  large  dial 
reads  eighteen  divi- 
sions, indicating  18 
feet.  The  total  read- 
ing of  the  anemome- 
ter is,  therefore, 
2,118  feet.  There 
is  a  small  catch  b  at  FlG-  15 

the  top  of  the  instrument  by  which  the  hands  of  the  dial  are 
thrown  out  of  or  into  gear  with  the  vane,  so  that  the  dial  hands 
may  be  started  or  stopped  at  any  time  while  the  vane  is 
moving  rapidly. 

Another  form  of  Biram  anemometer  is  shown  in  Fig.  15. 
This  is  entirely  similar  in  its  action  and  use  to  the  anemom- 
eter shown  in  Fig.  14;  a  handle  a  can  be  screwed  into  the 
bottom  of  the  base  b.- 

29.  Special  Anemometers. — The  special  form  of  self- 
timing  anemometer  shown  in  Fig.  16  does  away  with  the 


28 


MINE  VENTILATION 


§13 


use  of  a  watch,  since  the  reading  is  obtained  in  feet  per 
second.  It  works  on  an  entirely  different  principle  from 
the  ordinary  Biram  anemometer.  The  dial  contains  two 
graduated  circles  a  and  d,  which  are  continuous  in  their 
readings.  The  large  pointer  c  gives  the  reading  of  the 
instrument,  while  the  small  index  hand  d  shows  whether 
the  reading  is  to  be  taken  from  the  outer  or  the  inner  circle. 
The  instrument  is  held  with  its  back  to  the  air-current,  and 
when  the  vane  is  moving  rapidly  the  plunger  rod  e  is  sud- 
denly pushed  down,  thus 
releasing  the  pointers  c 
and  d,  which  immediately 
swing  around  to  positions 
indicating  the  velocity  of 
the  air-current,  in  feet  per 
second.  If  the  velocity 
exceeds  12  feet  per 
second,  the  reading  is 
taken  from  the  inner  cir- 
cle. The  instrument  will 
not  record  a  higher  ve- 
locity than  25  feet  per 
second.  This  instrument 
requires  but  a  moment's 
exposure  to  the  air-cur- 
rent to  ascertain  its  ve- 
FlG- 16  locity,  but  possesses  the 

disadvantage  that  an  average  reading  cannot  be  taken  in  an 
airway  where  the  velocity  is  not  uniform  in  all  parts  of  the 
airway.  The  instrument  will  only  indicate  the  velocity  of 
the  air  at  the  point  where  it  is  held  when  the  plunger  e  is 
depressed.  After  the  reading  has  been  taken,  the  small 
milled  head  /  is  screwed  down  until  the  plunger  e  is  released. 
The  milled  head  is  then  unscrewed  and  the  pointers  return  to 
their  original  position  at  zero. 


30.     Another  special  form  of  anemometer  designed  for 
velocities  exceeding  30  feet  per  second,  which  might  injure 


§13 


MINE  VENTILATION 


29 


the  ordinary  Biram  anemometer,  is  shown  in  Fig.  17.  This 
instrument  requires  no  further  explanation  than  that  given 
with  reference  to  the  Biram  anemometer.  Its  dial  is  read 
in  the  same  manner  as  that  instrument.  The  front  view, 
Fig.  17  (a),  of  the  instrument,  shows  the  dial  face,  and  the 
back  view,  Fig.  17  (b) ,  the  arrangement  of  the  vanes,  or 
blades,  which  are  constructed  on  the  principle  of  a  ventila- 
ting fan,  the  air  entering  at  the  center  of  the  back  of  the 
instrument  and  passing  out  at  the  circumference.  As  in  the 
Biram  anemometer,  the  instrument  is  provided  with  a  catch  a 


FIG.  17 

for  throwing  the  dial  hands  into  and  out  of  gear.  The 
instrument  is  exposed  to  the  air-current  for  any  given  length 
of  time,  and  its  reading  divided  by  the  time,  in  minutes,  gives 
the  velocity  of  the  air,  in  feet  per  minute. 

31.  Use  of  the  Anemometer. — In  using  the  anemom- 
eter, the  instrument  should  be  held  at  about  arm's  length 
from  the  body  of  the  observer  and  in  such  a  position  that  it 
is  constantly  exposed  to  the  full  force  of  the  air-current;  that 
is,  perpendicular  to  the  direction  in  which  the  air  is  traveling. 
The  instrument  is  not  to  be  held  in  one  position,  but  should  be 
moved  slowly  and  regularly  into  different  parts  of  the  airway 
so  as  to  obtain  the  average  velocity  of  air  in  the  airway.  The 
reason  for  this  is  that  the  velocity  of  the  air  is  always  greatest 


30  MINE  VENTILATION  §i:j 

in  the  center  of  the  airway  and  less  near  the  sides,  top,  or  bot- 
tom, where  it  is  retarded  by  the  friction  of  these  surfaces;  the 
velocity  is  the  least  in  the  corners  of  an  airway. 

An  observer,  when  measuring  air,  usually  stands  facing 
one  side  of  the  airway  and  a  little  off  from  the  center  of  the 
passage.  Holding  his  watch  in  one  hand  and  the  anemom- 
eter in  the  other  so  that  it  is  exposed  to  the  full  velocity 
of  the  air-current,  the  observer  starts  the  instrument  on 
the  minute,  and  then  moves  it  slowly  up  and  down  and  from 
side  to  side  in  a  continuous  line  or  arc  of  a  circle,  avoiding 
any  sudden  movements  and  remaining  as  still  as  possible 
himself  so  as  not  to  disturb  the  air-current  unnecessarily. 
If  the  observation  is  continued  for  2,  3,  or  5  minutes,  the 
total  reading  of  the  anemometer  is  divided  by  the  number  of 
minutes  to  obtain  the  velocity  of  the  air,  in  feet  per  minute. 

In  reading  the  anemometer,  an  allowance  may  be  made  by 
adding  to  the  reading  a  certain  constant  given  by  the  makers 
for  each  instrument;  this  constant  is  supposed  to  make  due 
allowance  for  the  inertia  of  the  instrument.  In  general  mine 
practice,  this  correction  is  unnecessary,  as  the  reading  of  the 
anemometer  gives  at  best  only  a  rough  approximation  of  the 
average  velocity  of  the  air-current,  owing  to  the  fact  that 
the  velocity  of  the  air  varies  in  different  portions  of  the  air- 
way. Again,  the  body  of  the  observer  occupies  a  certain 
portion  of  the  sectional  area  of  the  airway,  and  thus  slightly 
increases  the  velocity  of  the  moving  air  at  the  point  of  obser- 
vation. The  amount  of  this  increase,  however,  is  very  slight 
and  not  in  proportion  to  the  area  taken  up  by  the  body  of  the 
observer.  The  increase  of  the  velocity  due  to  this  cause  will 
help  to  compensate  for  the  inertia  of  the  instrument  without 
the  addition  of  the  constant  given  by  the  makers.  The  main 
point  to  be  observed  in  measuring  the  velocity  of  the  air  in 
any  given  airway  is  to  measure  always  in  the  same  place  and 
in  the  same  manner,  so  that  comparative  readings  will  be 
obtained,  regardless  of  whether  these  readings  are  somewhat 
low  or  high. 

In  many  states,  the  law  provides  when,  where,  and  bv  whom 
systematic  readings  with  the  anemometer  must  be  taken. 


§13 


MINE  VENTILATION 


81 


is,    therefore,   often 


TO    MEASURE    VENTILATING    PRESSURE 

32.  The  unit  of  ventilating  pressure  in  an  airway  is 
measured  by  the  water  column  it  will  support.  This  unit 
pressure,  in  pounds  per  square  foot, 
expressed  in  terms  of  a  water  column 
or  inches  of  water  gauge  as  it  is  called. 
If  a  cubical  box  measuring  1  foot  (12 
inches)  on  each  edge,  Fig.  18,  is  filled 
with  water;  the  capacity  of  the  box  is  1 
cubic  foot,  and  the  weight  of  the  water 
is  62.5  pounds.  When  the  box  is  filled, 
the  pressure  on  the  bottom  of  the  box 
is  equal  to  the  weight  of  the  water  FIG.  is 

(62.5  pounds);  in  other  words,  the  pressure  per  square  foot  due 
to  a  -water  column  1  foot  high  is  62.5  pounds.  If  the  water 

62  5 

in  the.  box  were  only  1  inch  deep,  its  weight  would  be  — 4- 

\2i 

=  5.2  Ib.  and  the  pressure  on  the  bottom  of  the  box  would 
then  be  equal  to  this  weight  of  water;  that  is,  the  pressure 
per  square  foot  due  to  an  inch  of  water  column  is  5.2  pounds. 
As  shown  in  the  figure,  the  weight  of  a  prism  of  water 

62.5 


having  a  base  of  1  square  inch  and  a  height  of  1  foot  is 


144 


=  .434  pound;  hence,   the  pressure  per  square  inch   due  to  a 
foot  of  water  column  is  .434  pound. 

33.  The  Water  Gauge. — The  ventilating  pressure  caus- 
ing the  circulation  of  air  in  a  mine  is  measured  by  an  instru- 
ment called  the  water  gauge,  which  consists  of  a  glass 
tube  bent  in  the  form  of  the  letter  U,  and  having  .both  arms  of 
the  tube  open  at  the  top  for  the  free  admission  of  the  air. 
The  glass  tube  is  firmly  attached  to  a  wooden  base  and  the 
upper  end  of  one  arm,  as  shown  in  Fig.  20,  is  bent  at 
a  right  angle  so  as  to  pass  through  the  wooden  back  and 
is  cemented  to  a  short  brass  tube.  In  Fig.  19,  C  and  D  rep- 
resent two  parallel  entries;  E  is  a  wooden  brattice  placed 
in  a  cross-cut  between  these  two  airways.  If  one  of  the 
airways  is  the  intake  and  the  other  the  return,  and  a  water 

145—13 


32  MINE  VENTILATION  §13 

gauge  A  is  placed  on  the  brattice  E,  so  that  the  extended 
arm  of  the  water  gauge  will  pass  through  a  hole  in  the 
brattice,  as  shown  at  B>  one  arm  of  the  gauge  will  be 
open  to  the  intake  pressure  while  the  other  is  open  to  the 


Fio.19 

return.  It  makes  no  difference  on  which  side  of  the  brattice 
the  water  gauge  is  placed.  The  intake  pressure  being  the 
greater,  will  always  depress  the  water  in  the  arm  of  the  tube 


to  which  it  has  access,  and  the  water  will  rise  in  the  arm 
open  to  the  return  pressure. 

In  Fig.  20  are  shown  three  forms  of  water  gauges  in  com- 
mon use,  which  differ  only  in  the  graduation  of  the  scale  by 
which  the  difference  in  the  level  of  the  water  in  the  two  arms 
of  the  gauge  is  measured.  The  simplest  of  these  scales, 


§13  MINE  VENTILATION  33 

shown  at  Fig.  20  (a)  has  its  zero  at  the  bottom  of  the  scale 
and  is  graduated  in  inches  and  tenths  of  an  inch.  This  scale 
must  be  adjusted  after  the  water  gauge  is  placed  in  position, 
and  the  water  has  come  to  rest  in  the  two  arms  of  the  tube. 
When  the  zero  of  the  scale  is  made  to  correspond  to  the 
lower  level  of  the  water  in  the  gauge,  the  upper  level  indi- 
cates the  inches  of  water  gauge,  from  which  the  ventilating 
pressure  is  calculated,  in  pounds  per  square  foot.  A  second 
form  of  scale  is  shown  in  Fig.  20  (b)  having  its  zero  at  the 
center  of  the  scale,  and  being  graduated  each  way  in  inches 
and  tenths  of  an  inch.  This  scale  should  be  adjusted  to  the 
level  of  the  water  in  each  arm  of  the  tube  before  the  gauge 
is  placed  in  position.  When  in  position,  the  level  of  the 
water  will  fall  in  one  arm  as  much  as  it  rises  in  the  other, 
and  the  sum  of  the  two  readings  in  this  case  is  the  total 
water-gauge  reading.  In  order  to  avoid  the  necessity  of 
taking  the  sum  of  the  two  readings,  a  third  scale,  shown  in 
Fig.  20  (c)  ,  is  sometimes  used,  having  its  zero  at  the  center 
and  being  graduated  both  ways  in  half  inches,  each  half  inch 
being  divided  into  five  equal  parts.  Since  each  half  inch  on 
this  scale  is  marked  as  a  whole  inch,  the  reading  of  either 
arm  of  the  gauge  represents  the  entire  water  column.  In 
each  of  these  three  scales,  the  reading  of  the  water  gauge 
is  2  inches. 

Since  each  inch  of  water  column  represents  a  pressure  of 
5.2  pounds  per  square  foot,  the  unit  of  ventilating  pressure 
in  any  case  is  found  by  multiplying  the  inches  of  water 
gauge  by  5.2. 

34.  Calculation  of  Water  Gauge.  —  Since  1  inch  of 
water  gauge  corresponds  to  a  pressure  of  5.2  pounds  per 
square  foot,  the  inches  of  water  gauge  i  produced  in  any  cir- 
culation are  equal  to  the  unit  of  ventilating  pressure,  pounds 
per  square  foot,  divided  by  5.2,  as  expressed  by  the  formula, 


The  pressure,  or  water  gauge,  increases  with  the  extent  of 
the  mine  workings,  other  things  being  equal,  since  the  mine 


34  MINE  VENTILATION  §13 

resistance  increases  as  the  workings  increase  in  extent  unless 
the  air  is  divided  into  separate  currents.  The  water  gauge 
depends  on  the  resistance  and  not  on  the  quantity  of  air. 

EXAMPLE  1. — What  is  the  water  gauge  corresponding  to  a  ventila- 
ting pressure  of  20.8  pounds  per  square  foot? 

SOLUTION.— Substituting  in  the  formula, 


i  =  J-  =  s0-8  = 


5.2  -   5.2 

EXAMPLE  2. — What  water  gauge  will  produce  a  velocity  of  600  feet 
per  minute  in  an  airway  8  ft.  X  10  ft.  and  2,500  ft.  long? 

SOLUTION. — The  unit  of  ventilating  pressure  in  this  circulation  is 
found,  from  the  formula, 

p  =  k-*f  =  ™^X2(WyQX2.™XWt  =  8'1  lb- per  sq.ft.; 
then,  substituting  this  value  in  the  formula  for  water  gauge, 

' 


CALCULATIONS  IN  VENTILATION 
35.  Degree  of  Accuracy. — The  volume  of  an  air- 
current  cannot  be  estimated  probably,  in  practice,  within 
100  cubic  feet  per  minute;  hence,  it  is  unnecessary  to  attempt 
to  calculate  the  volume  of  an  air-current  closer  than  that 
amount.  The  same  is  true,  even  to  a  greater  extent,  in 
regard  to  the  rubbing  surface  of  an  airway.  For  example, 
suppose  that  the  length  of  an  airway  8  ft.  X  10  ft.  meas- 
ures 2,510  feet.  The  actual  rubbing  surface,  in  this  case, 
is  2(8  +  10)2,510  =  90,360  square  feet;  but  except  in  very 
close  calculations,  and  when  comparing  the  circulations  of 
two  airways,  this  may  be  taken  as  90,000  square  feet  In  gen- 
eral, the  actual  calculated  rubbing  surface  may  be  increased 
or  decreased  to  the  extent  of  1  per  cent,  without  affecting 
the  practical  value  of  the  calculation. 

The  calculation  for  horsepower  should  be  carried  to  three 
decimal  places  for  less  than  100  horsepower;  but  two  deci- 
mal places  are  sufficient  when  the  power  exceeds  100  horse- 
power. In  general,  velocity  expressed  in  feet  per  minute 
requires  no  decimals;  water  gauge  should  be  read  to  hun- 
dreths  of  an  inch,  and  units  of  ventilating  pressure  less  than 


§13  MINE  VENTILATION  35 

10  pounds  per  square  foot  should  be  carried  to  two  decimal 
places,  but  for  10  pounds  per  square  foot  or  greater,  one 
decimal  place  is  sufficient.  In  discarding  figures,  if  the  first 
figure  of  those  discarded  reading  from  the  left  toward  the 
right  is  5  or  over  5,  1  should  be  added  to  the  last  figure  at 
the  right  of  those  retained.  Thus,  if  the  calculated  quantity 
is  507,605  cubic  feet,  508,000  cubic  feet  should  be  used;  but 
if  the  quantity  is  507,400  cubic  feet,  507,000  cubic  feet 
should  be  used. 

36.  Elementary  Formulas.  —  The  following  elemen- 
tary or  fundamental  formulas,  for  calculations  in  mine  ven- 
tilation and  the  methods  of  using  them  have  been  given  in 
the  articles  mentioned  in  connection  with  each  formula. 

For  rubbing  surface,  Art.  9, 

s  =  lo  (1) 

For  total  pressure,  Art.  12, 

P  =  pa  (2) 

For  quantity  of  air  per  minute,  Art.  16, 

g  =  av  (3) 

For  mine  resistance,  Art.  18, 

R  =  ksv*  (4) 

For  mine  resistance,  Art.  20, 

R  =  pa  (5) 

For  unit  of  ventilating  pressure,  Art.  22, 


p  =  --  (6) 

a 

For  units  of  work  per  minute,  Art.  24, 

u  =  pav  (7) 

and  u  =  ksif  (8) 

For  horsepower,  Art.  26, 


For  water  gauge,  Art.  34, 


36  MINE  VENTILATION  §13 

in  which   a  =  sectional  area  of  airway,  in  square  feet; 
h  —  horsepower; 
i  =  water  gauge,  in  inches; 
k  =  coefficient  of  friction  =  .00000002; 
/  =  length  of  airway,  in  feet; 
o  =  perimeter  of  airway,  in  feet; 
p  =  ventilating  pressure,  in  pounds  per  square  foot; 
P  =  total  ventilating  pressure,  in  pounds; 
q  =  quantity  of  air  in  circulation  in  cubic  feet  per 

minute; 

R  =  resistance  of  airway,  in  pounds; 
s  =  rubbing  surface  of  airway,  in  square  feet; 
u  =  units  of  power,  in  foot-pounds  per  minute; 
v  =  velocity  of  air  current,  in  feet  per  minute. 

37.  Transposition  of  Formulas.  —  Numerous  trans- 
positions of  the  formulas  in  Art.  36  may  be  made  so  as  to 
give  other  formulas  for  determining  the  factors  —  velocity, 
quantity,  etc.  —  appearing  in  the  formulas  in  other  terms  than 
those  used  in  the  fundamental  formulas.  For  example,  sup- 
pose that  it  is  desired  to  find  the  velocity  that  a  given  horse- 
power will  produce  in  a  given  airway.  None  of  the  elemen- 
tary formulas  contain  both  of  the  terms  h  and  v,  but  by 
combining  formulas  8  and  9  and  calling  the  required 
velocity  x,  its  value  is  determined  as  shown  in  the  following 
example: 

EXAMPLE  1.  —  Find  the  velocity  that  11.782  horsepower  will  produce 
in  an  airway  8  ft.  X  10  ft.  and  2,500  feet  long. 

SOLUTION.  —  The  rubbing  surface  of  this  airway,  as  determined 
by  the  formula  s  =  lo,  is  2,500  X  2(8  +  10)  =  90,000  sq.  ft.  Then, 
since  u  =  33,000  ht  multiplying  the  horsepower  by  33,000  reduces  it 
to  foot-pounds;  substituting  these  values  in  formula  8,  Art.  36, 
11.782  X  33,000  =  .00000002  X  90,000  X  v';  or,  388,800  =  .0018  »•;  then 

216,000,000,  and 


v  =  ^216,000,000  =  600  ft.  per  min.    Ans. 

EXAMPLE  2.  —  Find  the  quantity  of  air  that  will  pass  in  an  airway 
8  ft.  X  10  ft.  and  2,500  ft.  long,  under  a  water  gauge  of  1.56  inches. 

SOLUTION.  —  Find  the  pressure  corresponding  to  this  water  gauge 
by  multiplying  it  by  5.2  (Art.  33),  thus  p  =  5.2  X  i  =  5.2  X  1.56 


§  13  MINE  VENTILATION  37 

=  8.1  Ib.  per  sq.  ft.     Now,  finding  the  velocity  v  by  substituting  this 
value  for  p  in  the  formula  p  =  ,  and  making  the  rubbing  surface 

.00000002  X  90,000  X  v' 
as  before,  s  =  90,000  sq.  ft.,  8.1  =  —  —  and 

o  X  iU 

8.1  =  .0000225  v';  then  v'  =    Q^225  =  360,000,  and 

v  =  V360.000  =  600  ft.  per  rain. 

Finally,  finding  the  quantity  of  air  in  circulation  by  substituting  this 
value  for  v  in  the  formula  q  =  a  v, 

q  =  (8  x  10)  600  =  48,000  cu.  ft.  per  min.     Ans. 

38.  In  like  manner,  as  shown  in  the  last  two  examples, 
it  is  always  possible  to  substitute  the  given  values  in  the 
elementary  formulas  given  in  Art.  36  and  thus  obtain  any 
required  factor  of  a  ventilation  problem.  This  method  of 
calculation  greatly  reduces  the  number  of  formulas  that  it  is 
necessary  to  memorize.  There  are  two  formulas  that  can  be 
derived  from  those  already  given,  as  explained  above,  but 
which  it  is  convenient  to  memorize  as  they  are  so  frequently 
used.  These  are  the  formulas  for  obtaining  the  power  or 
pressure  required  to  pass  a  certain  quantity  of  air  in  a  given 
airway. 

Power. — Since  v  =  -  and  v*  =  — ,  this  value  can  be  sub- 
a  a3 

stituted  for  v*  in  the  formula  u  =  ksv*  giving, 

u  =  **£      (i) 

a 

Pressure. — Since  v  =  -  and  v'  =  — ,  this  value  can  be  sub- 
a  a 

stituted  for  z>a  in  the  formula  p  =  —^--  giving, 

a 

p  =  h*£       (2) 

a 

EXAMPLE  1.— What  quantity  of  air  will  be  circulated  by  11.782 
horsepower  in  an  airway  8  ft.  X  10  ft.  in  cross-section  and  2,500  feet 
long? 

SOLUTION.— The  area  a  of  the  airway  is  8  X  10  =  80  sq.  ft.;  the 
rubbing  surface  s  of  the  airway  is  2,500  X  2(8  +  10)  =  90,000  sq.  ft.;  the 


38  MINE  VENTILATION  §13 

power  u  =  33,000  h.     Then,  substituting  these  values  in  formula  1, 


33,000  X  11.782  =  ^000002x90^000X_?! 

80 
transposing  the  formula  and  extracting  the  cube  root 


=  80  X  600  =  48,000  cu.  ft.  per  minute.     Ans. 

EXAMPLE  2.  —  What  quantity  of  air  will  a  pressure  of  8.1  pounds 
per  square  foot  circulate  in  an  airway  8  ft.  X  10  ft.  and  2,500  feet 
long? 

SOLUTION.  —  The  area  and  perimeter  of  the  airway  are  the  same  as 
in  the  preceding  example.  Then,  substituting  the  given  values  in 

formula  2,  /  =  —  f-t 

.00000002  X  90,000  X  ?* 

80s 
transposing  the  formula  and  extracting  the  square  root 


80X8.1 


*  =  MX.  00000002X90.000  =  ^^'^ 

=  48,000  cu.  ft.  per  minute.     Ans. 

EXAMPLE.— A  current  of  48,000  cubic  feet  per  minute  is  circulated 
in  a  mine  by  a»pressure  of  8.1  pounds  per  square  foot.  If  the  size  of 
the  airway  is  8  ft.  X  10  ft.,  what  is  the  rubbing  surface  approxi- 
mately? 

SOLUTION.— The  area  is  the  same  as  in  the  preceding  examples; 
then,  substituting  the  given  values  in  formula  2,  p  =  — —-, 


.00000002  X  s  X  48,000s 
~~  80'~~ 


transposing  the  formula, 


39.  Although  any  of  the  problems  in  ventilation  can  be 
worked  by  means  of  the  fundamental  formulas  given  in 
Art.  36,  by  transposing  the  terms  of  one  formula  or  sub- 
stituting for  any  term  in  a  formula  its  equivalent  from 
another  formula,  it  is  convenient  to  have  the  formulas  tabu- 
lated as  given  in  Table  III,  so  that  when  it  is  desired  to  find 
any  particular  factor  of  a  ventilation  problem  the  formula  may 
be  quickly  obtained  by  consulting  the  table  and  finding  the 
desired  factor  in  terms  of  the  factors  given  in  the  problem. 


§13  MINE  VENTILATION  39 

No  attempt  should  be  made  to  memorize  all  of  these  for- 
mulas, and,  in  general,  it  will  be  found  best  to  depend  on 
transposition  of  and  substitution  in  the  elementary  formulas 
given  in  Art.  36,  but  for  reference  purposes  the  following 
tabulation  will  be  found  useful.  The  formulas  printed  in 
heavy  type  and  numbered  1  to  12  are  the  only  ones  that  need 
be  memorized. 

The  basis  for  the  calculations  is  an  airway  5  feet  wide 
by  4  feet  high  and  2,000  feet  long,  the  velocity  to  be  500 
feet  per  minute,  produced  by  a  pressure  of  9  pounds  per 
square  foot.  

PRACTICAL  PROBLEMS 

40.  There  are  two  general  classes  of  problems  in  mine 
ventilation.  The  first  class  considers  the  relation  existing 
between  the  factors  or  elements  of  a  single  airway,  as,  for 
instance,  the  power  or  the  pressure  required  to  produce  a 
certain  velocity  or  quantity  of  air  in  a  given  airway;  or  the 
question  may  be  reversed  and  ask,  what  velocity  or  quantity 
will  be  produced  in  a  given  airway  by  a  certain  power  or 
pressure.  In  examples  of  this  class,  the  solution  is  based  on 
the  unit  of  resistance  or  coefficient  of  friction.  For  example, 
multiplying  the  unit  resistance  (k  =  .00000002)  by  the  entire 
rubbing  surface  in  the  mine  or  airway  and  that  product  by 
the  square  of  the  velocity  gives  the  total  mine  resistance 
(ksv*  =  pa).  Dividing  the  mine  resistance  by  the  sectional 
area  of  the  airway  gives  the  unit  of  ventilating  pressure,  and 
dividing  this  by  5.2  gives  the  inches  of  water  gauge  required 
to  produce  the  given  velocity  in  this  mine  or  airway.  Or, 
multiplying  the  total  mine  resistance  (ksv*  =  pa]  by  the 
velocity  of  the  air-current  gives  the  work  per  minute  or  the 
power  required  to  produce  the  given  velocity  in  this  mine  or 
airway. 

The  second  general  class  of  problems  compares  the  circula- 
tion in  one  airway  with  that  in  another  airway;  for  instance,  the 
velocity  or  quantity  produced  by  a  given  power  or  pressure 
in  one  mine  is  compared  with  the  velocity  or  quantity  that 
the  same  power  or  pressure  will  produce  in  another  mine. 


40 


MINE  VENTILATION 


§13 


383 


sr     sr     sr     s* 


s     s 


E 

3 
I 

5]"*    ^ 

to  O 

i 


§13 


MINE  VENTILATION 


41 


<    i 


••Us 


o   ft,    ft, 


MINE  VENTILATION 


§13 


8       S8 


<         cb 

JO  o" 


"         X 


SI-*, 

II 


MINE  VENTILATION 


43 


I 


sr 

h 

0) 

a, 
S      X 

OS 


*      I 


<N  IO     <M 


^9      8s3  S? 


2  x 


<    <  .  -a      . 

d  a  5  1 
ill* 


.1 

Sj  8 
x  x 


su 


H-  -,  a 

•  8   W      ^         4* 

J6l       10      o        0, 


44 


MINE  VENTILATION 


§13 


"p 


in          *$ 


«  g  s 

£     <"     *? 


X 

8I§3  S 
H       H 


8" 


.S         2 

'a      'i 


13      O       ^ 

a     H      o 

"-t  N_^  p, 


»  »"e   I  % 
*  «l      |     IS 

1*3* 

a 


§13 


MINE  VENTILATION 


45 


•«i         -<i         •*«•*« 


46  MINE  VENTILATION  §13 

To  illustrate  the  application  of  the  foregoing  formulas,  a 
series  of  practical  examples  such  as  are  asked  at  examina- 
tions for  mine  foreman,  together  with  their  solutions,  will 
now  be  given.  By  paying  particular  and  careful  attention  to 
the  statements  of  the  examples  and  the  solutions  following 
them,  similar  ones  should  be  worked  without  trouble  by 
means  of  the  elementary  formulas  given  in  Art.  36  or  by 
transposing  them  as  explained  in  Art.  37. 


SINGLE    AIRWAYS    OR    CIRCULATIONS 

41.  The  following  examples  relate  to  single  airways 
or  circulations  of  air.  The  velocity,  quantity,  pressure, 
and  other  factors  of  the  airway  or  circulation  in  these  exam- 
ples, are  calculated  from  the  value  of  the  unit  resistance 
(k  =  .00000002). 

EXAMPLE  1.— In  an  airway  8  ft.  X  9  ft. ,  and  5,000  feet  long,  including 
the  return:  (a)  find  the  resistance  of  the  airway  for  a  velocity  of  480 
feet  per  minute;  (b)  find  the  quantity  of  air  passing  in  the  airway; 
(c)  find  the  unit  of  ventilating  pressure,  (d)  What  is  the  power  on 
the  air,  expressed  in  foot-pounds  per  minute?  (e)  What  is  the  horse- 
power of  the  circulation? 

SOLUTION.— (a)  K  =  ksv*  =  .00000002  X  2  (8  +  9)  5,000  X  480" 
=  783.36  Ib.  Ans. 

(b)  q  =  av  =  (8  X  9)  480  =  34,560,  say  34,600  cu.  ft.  permin.     Ans. 

r>          7QQ  Qft 

(c)  P  =  ~  =  f^f  =  10-88  Ib.  per  sq.  ft.     Ans. 

(d)  Since  R=pa,  its  value,  substituted  for  pa  in  the  following 
formula,  gives  u=pav  =  783.36  X  480  =  376,013,  say  376,000  ft.-lb. 
per  min.     Ans. 

Or,  another  way,  taking  the  values  q  =  34,600  and  p  =  10.88,  « 
=  qp  =  34,600  X  10.88  =  376,448,  say  376,000  ft.-lb.  permin.  Again,  in 
another  way,  u  =  k  s  v3  =  .00000002  X  2  (8  +  9)  5,000  X  4803  =  376,013, 
say  376,000  ft.-lb.  per  min. 

,  .  u  376,000 

W     k  =  337)06  =   337)00  =  11'394H-P-     ^ 

EXAMPLE  2. — If  the  velocity  of  the  air-current  is  550  feet  per  minute 
in  an  airway  6  ft.  X  10  ft.,  what  is  the  quantity  of  air  in  circulation? 

SOLUTION. —    q  -  a  v  =  (6  X  10)  550  =  33,000  cu.  ft.  per  min.    Ans. 

EXAMPLE  3. — If  the  mine  resistance  is  1,000  pounds  in  an  airway 
8  ft.  X  10  ft.,  what  is  the  water  gauge  produced  by  the  circulation? 


§13  MINE  VENTILATION  47 

12.5  Ib.  per  sq.  ft. 


then,  *  =  f^  =  y|  =  2-4  in-     Ans- 

EXAMPLE  4. — What  velocity  will  15  horsepower  produce  in  an  air- 
way 6  ft.  X  10  ft.,  and  3,000  feet  long? 

SOLUTION.—  «  =  33,000  h  =  33,000  X  15  =  495,000  ft.-lb.  per  min. 
Then,  since  u  =  ksv3,  by  substituting  values  and  calling  the  required 
velocity  v, 

495,000  =  .00000002  X  2(6  +  10)  3,000  X  v3 


and  495,000  =  .00192  v3,  and  v3  =  ~f       =  257,812,500 

.uuiy^ 

v  =  ^257,812,500  =  636+  ft.  per  min.     Ans. 

EXAMPLE  5.—  What  is  the  area  of  an  airway  in  which  a  current  of 
60,000  cubic  feet  of  air  is  passing  per  minute,  if  the  velocity  of  the  air 
is  10  feet  per  second? 

SOLUTION.—  In  this  case,  v  =  60  X  10  =  600  ft.  per  min.,  and  sub- 
stituting values  in  the  formula,  q  =  a  v,  calling  the  required  area  a, 
60,000  =  600  a,  and 

,.    Ans. 


EXAMPLE  6.  —  Calculate  the  approximate  amount  of  rubbing  sur- 
face in  a  mine  in  which  it  is  assumed  the  coefficient  of  friction  is 
k  =  .00000002  when  the  sectional  area  of  the  airway  is  60  square  feet  and 
a  current  of  40,000  cubic  feet  of  air  is  passing  per  minute  under  a  3-inch 
water  gauge. 

SOLUTION.  —  The  unit  of  ventilating  pressure  corresponding  to  a 
3-in.  water  gauge  is  p  =  3  X  5.2  =  15.61b.  per  sq.  ft.;  transposing  the 

k  s  q*  pa3 

formula  p  =  —  f-,  s  =  J-L—.. 
a  kg 

15.6  X  60  X  60  X  60 

=  105'300'  *'•  about  m'm  sq    ft 


a 

Ans. 

EXAMPLE  7.  —  What  quantity  of  air  is  passing  down  a  shaft  12  feet 
in  diameter  when  the  current  has  a  velocity  of  325  feet  per  minute? 

SOLUTION.  —  Since  the  diameter  is  specified,  the  shaft  is  evidently 
circular. 

q  =  a  v  =  12'  x  .7854  X  325  =  36,756.72  cu.  ft.  per  min.,  or  say 
37,000  cu.  ft.     Ans. 

EXAMPLE  8.—  Where  the  airway  is  12  feet  wide  at  the  bottom, 
10  feet  4  inches  wide  at  the  top,  and  6  feet  6  inches  high,  and  the 
velocity  of  the  air  is  340  feet  per  minute,  what  is:  (a)  the  sectional 
a-rea  of  the  airway;  (b)  the  quantity  of  air  passing  per  minute? 

145—14 


48  MINE  VENTILATION  §13 

SOLUTION.  —  (a)  The  section  is  a  trapezoid;  hence,  since  4  in.  =  ift., 
and  6  in.  =  £  ft. 


(b)  q  =  a  v  =  72A  X  340  =  24,678£  cu.  ft.  per  min.  or  say  25,000 
cu.  ft.  Ans. 

EXAMPLE  9.—  If  a  shaft  8  ft.  X  24  ft.  in  section  is  the  intake,  and 
the  fan  is  exhausting  160,000  cubic  feet  of  air  per  minute,  what  is  the 
velocity  of  the  air-current  in  the  shaft? 

SOLUTION.  —  Transposing  the  formula  q  =  a  v, 

An, 


EXAMPLE  10. — An  air-course  is  500  yards  long,  6  feet  high,  and 
7  feet  wide;  what  is:  (a)  its  sectional  area?  (£)'its  perimeter?  (c)  its 
rubbing  surface? 

SOLUTION.— (a)  Sectional  area  a  =  6  X  7  =  42  sq.  ft.     Ans. 

(6)     Perimeter  o  =  2(6  +  7)  =  26  ft.     Ans. 

(c)     Rubbing  surface  s  =  lo  =  500  X  3  X  26  =  39,000  sq.  ft.     Ans. 

EXAMPLE  11. — The  rubbing  surface  of  an  airway  is  25,000  square 
feet  and  the  perimeter  50  feet;  what  is  the  length? 

SOLUTION. — Transposing  the  formula  s  =  lo, 

25,000 

—~~—  =  500  ft.     Ans. 
ou 

EXAMPLE  12. — When  the  water-gauge  is  1.85  inches,  what  pressure 
per  square  foot  does  it  indicate? 

SOLUTION.— Transposing  the  formula  *  =  £=, 

o.z 

p  =  5.2  i  =  5.2  X  1.85  =  9.62  Ib.  per  sq.  ft.     Ans. 

EXAMPLE  13.— What  is  the  total  ventilating  pressure  of  an  airway 
6  ft.  X  7  ft.,  the  water  gauge  being  .5  inch? 

SOLUTION. — Pressure  per  square  foot  =  5.2  X  .5  =  2.6  Ib.;  area 
=  6  X  7  =  42  sq.  ft. 

P  =  pa  =  2.6X42  =  109.2  Ib.     Ans. 

EXAMPLE  14. — If  80,000  cubic  feet  of  air  is  required  per  minute  in 
a  mine,  and  the  shaft  velocity  must  not  exceed  800  feet  per  minute, 
what  is  the  smallest  sectional  area  that  the  shaft  may  have? 

SOLUTION. — Transposing  the  formula  q  =  a  v, 

a  =  -  =  —^fr  =  1Q0  s<3-  ft-     Ans- 
V  oUO 


§13  MINE  VENTILATION  49 


SPECIAL    CALCULATIONS 

42.  Regulator  Calculations. — A  regulator  placed  in 
an  airway  offers  a  certain  resistance  to  the  passage  of  the 
air-current.  This  resistance  is  added  to  the  resistance  of 
the  airway  and  therefore  it  has  the  same  effect  as  would  be 
produced  by  increasing  the  length  of  the  airway;  that  is,  it 
increases  the  mine  resistance.  The  amount  of  air  passing 
through  the  regulator  depends  on  the  size  of  the  opening; 
the  smaller  the  opening,  the  smaller  is  the  quantity  of  air 
passing  under  the  same  pressure. 

In  the  use  of  a  regulator,  two  pressures  are  considered: 
the  natural  pressure  due  to  the  frictional  resistance  of  the 
airway  and  the  pressure  due  to  the  regulator.  The  sum  of 
these  two  pressures  is  the  unit  of  ventilating  pressure  on  the 
air  at  the  mouth  of  the  airway;  this  is  true  whether  the  regu- 
lator be  placed  at  the  mouth  or  at  the  end  of  the  airway. 

The  amount  of  the  opening  in  a  box  regulator  is  determined, 
practically,  by  moving  the  shutter  backwards  or  forwards 
until  the  desired  amount  of  air  is  obtained,  but  it  is  possible 
to  calculate  the  quantity  of  air  that  will  pass  through  any  size 
of  opening  in  the  regulator  when  the  pressure  due  to  the 
regulator  is  known.  To  find  this  pressure,  it  is  first  neces- 
sary to  calculate  the  pressure  due  to  the  frictional  resistance 
of  the  airway  when  the  desired  quantity  of  air  is  passing,  by 
substituting  the  values  for  the  length,  perimeter  and  area  of 
the  airway  and  the  desired  quantity  of  air  in  the  formula 

p  =  -—-.     The  pressure  thus  found  is  subtracted  from  the 
a 

mine  pressure  at  the  mouth  of  the  airway,  as  shown  by  the 
water  gauge,  and  the  difference  or  remainder  is  the  pressure 
due  to  the  regulator.  Dividing  this  pressure  by  5.2  will  give 
the  inches  of  water  gauge  due  to  the  regulator,  which  is 
theoretically  the  reading  of  a  water  gauge  placed  on  the  regu- 
lator, not  too  close  to  the  opening,  but  about  midway  between 
the  opening  and  the  rib  or  side  of  the  airway.  This  water- 
gauge  reading  indicates  the  difference  of  pressure  between 
the  intake  and  the  return  sides  of  the  regulator. 


50  MINE  VENTILATION  §  13 

The  quantity  of  air  q  in  cubic  feet  per  minute  that  will 
pass  through  an  opening  whose  area  is  a,  in  square  feet, 
under  a  water  gauge  z,  in  inches,  is  given  by  the  formula, 

?  =  2,630  a  V*  (1) 

To  find  the  area  of  an  opening  that  will  pass  any  required 
quantity  of  air  under  a  given  water  gauge,  this  formula  is 
written, 

a  =  .00038  -3-          (2) 

Vz 

The  use  of  these  formulas  is  shown  by  the  following 
examples: 

EXAMPLE  1.  —  What  quantity  of  air  will  pass  each  minute  through  a 
regulator  having  an  opening  2  ft.  X  3  ft.,  when  the  water-gauge  read- 
ing taken  on  the  regulator  is  2.5  inches? 

SOLUTION.  —  Substituting  the  given  values  in  formula  1,  the  quantity 
of  air  passing  through  the  regulator  is 

q  =  2,630(2  X  3)  V2~5  =  24,950,  say  25,000  cu.  ft.     Ans. 

EXAMPLE  2.  —  Find  the  area  of  the  opening  in  a  regulator  placed  in 
an  airway  6  ft.  X  8  ft.  in  section  and  2,000  feet  long,  so  as  to  reduce 
the  quantity  of  air  passing  in  this  airway  to  30,000  cubic  feet  per 
minute.  The  ventilating  pressure  at  the  mouth  of  this  airway  is 
15  pounds  per  square  foot. 

SOLUTION.—  The  perimeter  of  this  airway  is  2(6  +  8)  =  28  ft.,  and 
the  area  6  X  8  =  48  sq.  ft.;  the  rubbing  surface  is  2,000  X  28  =  56,000 

sq.  ft.     Substituting  the  given  values  in  the  formula  p  =  —  ~  to  find 

the  natural  pressure  due  to  the  circulation  of  30,000  cu.  ft.  of  air  in 
this  airway, 

f  _  .00000002X^.000X30,000. 

Subtracting  this  natural  pressure  from  the  mine  pressure  at  the 
mouth  of  the  split,  and  dividing  by  5.  2,  the  water-gauge  reading  at  the 

regulator  is,  i  =  —          —  =  1.13  in.;  and,  finally,  substituting  values 
DJB 

in  formula  2, 


a  =  .00038  =  io.72  sq.  ft.    Ans. 

Vl.13 

EXAMPLE  3.  —  If  5,000  cubic  feet  of  air  is  passing  each  minute 
through  a  regulator  and  there  is  a  difference  of  $  inch  in  the  water- 
gauge  readings  on  the  two  sides  of  the  regulator,  how  far  is  the 
regulator  slide  open  if  the  opening  in  the  regulator  is  2  feet  high? 


§13  MINE  VENTILATION  51 

SOLUTION.  —  Substituting  in  formula  2, 

.  -.  OOQ38  ^  ~-00038?6'00°  =  3.8  sq.ft. 

\i  -D 

If  the  height  of  the  opening  is  2  ft.,  the  width  will  be  ~  =  1.9  ft. 

Ans. 

43.     Quantity  Produced  by  Two  or  More  Ventilators. 

In  the  development  of  a  mine,  it  often  happens  that  the  means 
used  for  producing  a  ventilating  current  becomes  inadequate 
for  the  production  of  the  quantity  of  air  required  as  the 
extent  of  the  workings  increases.  To  increase  the  circula- 
tion, it  is  often  proposed  to  duplicate  the  ventilating  appara- 
tus in  use  by  adding  another  fan  or  furnace  similar  to  the 
one  already  in  operation.  This  means  an  increase  of  ven- 
tilating power,  which,  of  course,  produces  an  increase  of  the 
quantity  of  air  in  circulation.  Assuming  that  no  change  is 
made  in  the  course  of  the  circulation  of  the  air  through  the 
mine,  any  increase  of  quantity  will  require  an  increase  of 
power  in  proportion  to  the  cube  of  the  ratio  in  which  the 
quantity  is  increased,  as  is  shown  by  the  following  compar- 
ison of  power  and  quantity  for  a  given  airway: 

If  #!  represents  the  power  on  the  air  for  a  given  airway 
when  a  quantity  q*  is  circulating,  using  formula  1,  Art.  38, 


if  u3  represents  the  power  on  the  air 
a  a 

when  a  quantity  q3  is  circulating  through  the  same  airway, 
then, 


u, 


As  the  same  airway  is  considered  in  each  case,  k,  s,  and  a 

are  the  same  and  by  canceling,  —  =  -—  or  u^  :  u,  =  a*  :  g,'\ 

u.       q? 

that  is,  for  the  same  airway,  the  power  is  proportional  to 
the  cube  of  the  quantity,  or  the  ratio  between  the  powers  for 
two  quantities  of  air  equals  the  cube  of  the  ratio  between 


52  MINE  VENTILATION  §13 

the  quantities.  For  example,  if  the  quantity  is  to  be  doubled, 
the  quantity  ratio  is  then  2  and  the  power  ratio  is  23  =  8. 
That  is  to  say,  it  will  require  eight  times  the  power  to  double 
the  quantity  of  air  in  the  same  mine  or  airway.  This  shows 
that  two  fans  of  the  same  size  and  running  at  the  same  speed 
will  not  produce  double  the  quantity  of  air  circulated  by  one 
of  these  fans  alone. 

When  two  or  more  ventilating  motors  are  employed,  it  is 
evident  that  the  total  power  producing  the  circulation  is  equal 
to  the  sum  of  the  powers  of  the  several  motors. 

Now,  calling  the  quantities  produced  by  several  motors 
working  separately  on  the  same  airway  gly  g,,  etc.,  the  powers 
of  these  several  motors  «,,#„,  etc.,  and  the  total  quantity 
produced  when  all  the  motors  are  working  together,  Q, 

*2\  +  gf(k*\  +  etc.     Or,  dividing  both  mem- 
a3/  \a*/ 

bers  of  the  equation  by  — y,  Q*  =  q*  +  g,*  +  etc.,  and,  finally, 
a3 


Q  =  %3  -I-  g,3  +  etc. 

This  formula  shows  the  quantity  of  air  produced  by  the  com- 
bined action  of  two  or  more  ventilating  motors  working  on 
the  same  mine  or  airway,  and  which,  when  working  alone,  pro- 
duce the  quantities  glt  g^,  etc.  in  the  same  mine  or  airway. 

EXAMPLE. — A  fan  ventilating  a  certain  mine  is  capable  of  producing 
42,600  cubic  feet  of  air  when  operated  alone,  and  another  fan  venti- 
lating the  same  mine  will  produce  57,400  cubic  feet  when  working 
alone;  what  quantity  of  air  will  be  produced  in  this  mine  when  both 
fans  are  in  operation,  assuming  that  the  general  conditions  in  the  mine 
remain  the  same? 

SOLUTION. — Substituting  the  given  quantities  in  the  formula,  and 
calling  the  unknown  quantity  x ,  the  total  quantity  of  air  produced  by 
the  combined  action  of  the  two  fans 


x  =  \42,6003  +  57.4003  =  64,300  cu.  ft.  per  min.     Ans. 


COMPARING    DIFFERENT    CIRCULATIONS 

44.  The  following  examples  will  serve  to  illustrate  the 
method  of  calculation  to  be  employed  when  the  circulation  in 
one  mine  or  airway  is  compared  with  that  in  another  mine  or 


§13  MINE  VENTILATION  53 

airway.  For  example,  suppose  that  10  horsepower  is  cir- 
culating 50,000  cubic  feet  of  air  in  an  8'  X  12'  airway  of  a 
certain  length.  It  is  possible  from  these  data  to  calculate 
the  power  that  would  pass  the  same  quantity  of  air  in  a 
6'  X  8'  airway  of  twice  the  length.  Or,  it  is  possible  to  find 
the  quantity  of  air  the  same  power  will  produce  in  an  airway 
8  feet  square  of  any  given  length.  Such  problems  as  these 
are  sometimes  calculated  by  first  completing  the  data  relating 
to  the  first  mine  .or  circulation  by  the  use  of  the  methods 
explained  in  the  previous  examples,  and  then  calculating 
the  required  power  or  quantity  in  the  second  mine  or  cir- 
culation by  applying  the  same  methods  to  this  mine.  For 
example,  in  the  first  case  given,  the  length  of  the  airway  is 
not  given,  but  may  be  found  by  substituting  the  given  values 

in  the  formula  u  =  — *-.     Having  found  the  length  of  this 
a3 

airway,  that  of  the  second  airway  is  made  twice  this  length, 
and  the  power  required  to  circulate  the  same  quantity  of  air 
is  then  found  by  substituting  the  values  for  the  other  airway 
in  the  same  formula,  as  has  been  explained.  While  this 
method  of  calculation  is  simple,  it  is  long  and  cumbersome, 
and  the  method  now  to  be  explained  has  the  advantage  of 
permitting  the  cancelation  of  all  factors  common  to  both  air- 
ways, thus  greatly  reducing  the  work  of  the  calculation. 

In  comparing  two  or  more  airways,  it  is  necessary  to 
remember  that  a  change  in  the  sectional  area  of  an  airway 
may  or  may  not  be  accompanied  by  a  change  in  the  rubbing 
surface.  For  example,  an  8'  X  12'  airway  3,000  feet  long 
has  the  same  rubbing  surface  as  a  6'  X  9'  airway  4,000  feet 
long,  although  the  first  airway  has  an  area  of  96  square 
feet,  while  the  second  airway  has  an  area  of  only  54  square 
feet.  Again,  a  4'  X  12'  airway  of  any  length  has  the  same 
rubbing  surface  as  an  airway  8  feet  square  of  the  same  length, 
although  the  area  of  the  first  airway  is  48  square  feet,  while 
that  of  the  second  airway  is  64  square  feet. 

In  comparing  two  or  more  airways,  the  same  symbols  will 
be  used  to  indicate  .the  same  factors  in  different  airways, 
but  a  small  subscript  figure  will  indicate  the  airway  to  which 


54  MINE  VENTILATION  §13 

the  factor  belongs.  Thus,  the  power  applied  to  airways  1,2,3, 
etc.  is  written  ult  ut,  u3,  etc.  In  like  manner,  the  lengths 
of  these  airways  are  indicated  by  /,,  /2,  /3,  etc.;  the  perimeters 
by  <?i,  Ot,  03,  etc.;  the  areas  by  a,,  a,,  a3,  etc.  When  the 
symbol  is  written  without  a  subscript,  this  indicates  that  its 
value  is  the  same  for  all  the  airways  being  compared. 


POWER 

45.  Relation   Bet-ween   the   ^Length   of   an   Airway 
and    the    Power. — The   formulas    expressing    the    powers 
required  to  produce  the  same  velocity  in  two  airways  having 
the  same  cross-section  but  different  lengths  are  as  follows, 
substituting  lo  for  s  in  the  formula  u  =  ksv*: 

«!  =  k^ov*  (a) 

and  ut  =  kl*ov3  (b) 

Dividing  equation  (a)  by  equation  (&),  member  by  mem- 
ber, and  canceling  the  common  factors, 

«i  =  L 

u,       /, 

This  shows  that  the  ratio  between  the  powers  required  to 
produce  the  same  velocity  in  these  airways  is  equal  to  the 
ratio  between  the  lengths  of  the  airways;  or,  briefly  stated, 
the  power  ratio  is  equal  to  the  length  ratio  of  the  airways. 

Instead  of  being  expressed  as  a  ratio,  this  relation  may 

be  stated  as  a  proportion  since  —  =  —  is  merely  another 

way  of  expressing  the  proportion  ul  :  u,  —  /,  :  /2;  that  is,  for 
the  case  given,  the  powers  are  directly  proportional  to  the 
lengths  of  the  airways.  Similarly,  all  the  ratios  given  in  the 
following  articles  may  be  expressed  as  proportions,  but  for 
purposes  of  calculation  the  expression  by  ratios  has  some 
advantages  and  will  therefore  be  used.  The  terms  power 
ratio,  length  ratio,  etc.  are  used  as  abbreviations  for  the 
expressions  ratio  between  the  powers  of  two  airways,  ratio 
between  the  lengths  of  two  airways,  etc. 

46.  Relation  Between  Perimeter  and  Power. — The 

powers  required  to  produce  the  same  velocity  in  two  airways 


§13  MINE  VENTILATION  55 

having  the  same  lengths  but  different  perimeters  are  expressed 
by  the  formulas,      Ui  =  klo^  (fl) 

and  «,  =  klo,v*  (d) 

Dividing  equation  (a)  by  equation  (b),  as  before,  member 
by  member,  and  canceling  the  common  factors, 

Hi  —  *! 

U*          O, 

This  expression  shows  that  the  ratio  of  the  powers  required 
to,  produce  the  same  velocity  in  these  airways  is  equal  to 
the  ratio  of  the  perimeters  of  the  airways;  in  other  words, 
the  power  ratio  is  equal  to  the  perimeter  ratio. 

47.     Relation    of   Velocity   or    Quantity    to   Power. 

The  powers  required  to  produce  different  velocities  in  the 
same  airway  are  expressed  by  the  formulas, 

#!  =  klov?  (a) 

and  «2  =  klovS  (b) 

Dividing  equation  (a)  by  equation  (£),  member  by  mem- 
ber and  canceling  the  common  factors, 


v 

This  expression  shows  that  the  ratio  of  the  powers  required 
to  produce  different  velocities  in  the  same  airway  is  equal 
to  the  cube  of  the  ratio  of  the  velocities;  in  other  words,  the 
power  ratio  is  equal  to  the  cube  of  the  velocity  ratio.  In  like 
manner,  it  may  be  shown  that  the  power  ratio  is  equal  to  the 
rubbing  surface  ratio.  Ui  Si 

ut       s, 

48.  Relation  Between  Area  and  Power.  —  The  powers 
required  to  produce  the  same  quantity  in  two  airways  hav- 
ing the  same  length  and  perimeter  but  different  areas  are 
expressed  by  the  following  formulas  obtained  by  writing  lo 

for  .$•  in  the  formula  u  =     s<* 


to 

a,' 
h  i  »„* 

and  ut  •• 


56  MINE  VENTILATION  §  13 

Dividing  equation  (a}  by  equation  (b} ,  member  by  member, 
and  canceling  the  common  factors, 

w,  _  kloq*  _._  k log" .        «i  _  kloq*          a*      _  a* 
ut          a*  a*  u,  'a*          kloq*        a* 


«,  _   /«A- 
«,  ~   \aj 


This  expression  shows  that  the  ratio  between  the  powers 
required  to  produce  the  same  quantity  in  these  airways  is 
equal  to  the  cube  of  the  inverse  ratio  of  the  sectional  areas 
of  the  airways;  in  other  words,  the  power  ratio  is  equal  to  the 
cube  of  the  inverse  area  ratio. 

In  like  manner,  it  may  be  shown  that  the  power  ratio  is 
equal  to  the  cube  of  the  quantity  ratio. 


49.  General  Power  Ratio.  —  In  the  above  explanation, 
in  order  to  show  the  effect  of  each  factor  separately,  it  was 
assumed  that  one  element  only  changed  at  a  time,  the  other 
elements  being  the  same  for  each  airway.  If  all  the  factors 
in  the  two  airways  are  different  and  the  quantities  of  air  in 
circulation  and  the  powers  producing  the  circulations  in  the 
two  airways  are  also  different, 

k  /,  0i  q?  i   \ 

«i  =  -  ~^-  (a) 

&» 

kl.o.q?  ,,v 

«,  =  -  (b) 

a, 

Dividing  equation  (a)  by  equation  (£),  member  by  mem- 
ber, and  canceling  the  common  factors, 

&        &  x  ft  x  £,'  x  «/ 

ut        /*       o,       g3        a* 


g, 

This  is  a  general  expression  for  comparing  the  powers 
producing  the  circulation  in  any  two  airways.  It  shows 
that,  in  every  case,  the  power  ratio  is  equal  to  the  continued 
Product  of  the  length  ratio,  perimeter  ratio,  the  cube  of  the  quan- 
tity ratio,  and  the  cube  of  the  inverse  area  ratio.  Each  of  these 


§13  MINE  VENTILATION  57 

ratios  acts  separately,  and  the  value  of  any  one  of  them  may 
become  1,  if  the  value  of  that  factor  is  the  same  in  each 
airway.  If  the  length,  perimeter,  and  area  of  the  two  air- 
ways are  the  same,  these  ratios  each  become  1,  and  the 
power  ratio  is  then  equal  to  the  cube  of  the  quantity  ratio 
as  previously  stated.  Art.  48. 

A  comparison  of  the  circulations  in  two  airways  as  illus- 
trated shows  clearly  the  effect  of  each  factor  of  the  formula. 
For  example,  it  shows  in  what  proportion  the  power  increases 
with  respect  to  the  length  of  the  airway  for  a  constant 
velocity,  or  in  what  proportion  the  power  increases  with 
respect  to  the  rubbing  surface  for  a  constant  velocity,  or  how 
a  change  in  the  sectional  area  of  an  airway  affects  the  quan- 
tity 'of  air  in  circulation,  the  power  or  the  pressure  being 
constant.  Expressed  as  a  proportion,  the  preceding  expres- 
sion shows  that  when  the  other  factors  in  the  formulas  for 
the  two  airways  are  the  same,  the  powers  on  two  airways 
are  directly  proportional  to  lengths;  directly  proportional  to 
the  perimeter;  inversely  proportional  to  the  cubes  of  the 
quantities;  and  inversely  proportional  to  the  cubes  of  the 
areas.  A  few  examples  will  show  the  use  of  the  general 
expression  for  comparing  the  powers  of  two  airways. 

EXAMPLE  1. — If  100  horsepower  is  required  to  circulate  a  given 
quantity  of  air  in  an  airway  6  ft.  X  12  ft.  and  4,000  feet  long,  what 
horsepower  will  be  required  to  produce  the  same  circulation  in  an  air- 
way 8  ft.  X  10  ft.  and  2,000  feet  long? 

SOLUTION. — Calling  the  required  power  x  and  writing  the  given 
values  for  the  power,  length,  perimeter,  and  area  of  each  of  these  air- 
ways as  follows  and  omitting  the  quantities,  which  are  the  same  for 
each  airway: 

POWER    LENGTH    PERIMETER    QUANTITY    AREA 
First  airway  ....    100          4,000  36  72 

Second  airway  .    .    .     x  2,000  36  80 

Substituting  these  values  in  the  general  expression, 
x        2,000       36  /72\ 3 


100       4,000X36\80y 

NOTE.— It  is  always  simpler  to  write  the  unknown  quantity  x  as  the  numerator  of 
the  ratio  in  which  it  occurs,  which  in  this  case  makes  the  subscript  figures  1  refer  to 
the  second  airway,  while  the  subscript  figures  2  refer  to  the  first  airway.  The  sub- 
script figures  1  do  not  necessarily  mean  the  first  airway  or  the  subscript  figures  2  the 
second  airway,  but  these  figures  merely  indicate  different  airways. 


58  MINE  VENTILATION  §13 

the  perimeter  ratio  reduces  to  1,  because  these  values  of  o,  and  02  are 
equal.     Then,  canceling  the  common  factors  and  reducing, 

roo  =  K^)  =  \ x  im  =-  -3645>  and 

x  =  100  X  .3645  =  36.45  H.  P.     Ans. 

EXAMPLE  2.— If  60,000  cubic  feet  of  air  be  circulated  in  an  airway 
8  feet  square  and  2,500  feet  long,  what  quantity  will  the  same  power 
circulate  in  an  airway  6  ft.  X  8  ft.  and  3,000  feet  long? 

SOLUTION.— Calling  the  required  quantity  x,  and  writing  the  given 
values  for  the  quantity  of  air  and  the  length,  perimeter,  and  area  of  the 
airway,  and  omitting  the  powers,  which  are  the  same  for  each  airway, 

POWER     LENGTH      PERIMETER     QUANTITY         AREA 
First  airway  .   .   .  2,500  32  60,000  64 

Second  airway  .    .  3,000  28  x  48 

Substituting  these  values  in  the  same  expression,  and  remembering 
that  in  this  case,  the  power  being  the  same  in  each  airway,  the  power 
ratio  is  1, 

i  _3,000       28  /     x  64\» 

2,500  X  32  \60.000  X  48/ 
Then,  canceling  the  common  factors, 

i-6xZ  /_*_ _x4\-_a 

5  X  8  \60,000  X  3/         20 
Extracting  the  cube  root  of  each  member, 


and,  finally, 

x  =  —         —  =  44,267,  or  about  44,300  cu.  ft.  per  min.     Ans. 
.uuuu/zoy 

EXAMPLE  3. — If,  a  current  of  28,000  cubic  feet  of  air  per  minute  is 
passing  in  an  airway  6  ft.  X  7  ft.,  what  quantity  will  the  same  power 
pass  in  an  airway  5  feet  square  having  the  same  length? 

SOLUTION. — Here,  the  power  and  the  length  of  the  airway  are  the 
same  in  each  case  and  their  ratios  reduce  to  1.  The  perimeter  of  the 
first  airway  is  2(6  +  7)  =  26  ft.;  and  that  of  the  second  airway  2(5  +  5) 
=  20  ft.;  the  area  of  the  first  airway  is  6  X  7  =  42  sq.  ft.,  and  that  of 
the  second  airway  5  X  5  =  25  sq.  ft.  Hence,  calling  the  required  quantity 
of  air  circulating  in  the  second  airway  x,  and  substituting  the  given 

values  in  the  general  expression,  1  =  1  X  5^(90  nnn  ^  9~)   •     Cancel- 


, 

ing  the  common  factors,  1  =  TO  L  QQQ  x  05)   •    Multiplying  both  mem- 
bers of  this  equation  by  ^  gives  ^  =  —  X  ^  (^Q^)   •   Then  extracting 


§13  MINE  VENTILATION  59 

the  cube  root  of  both  members,  -\/~  =  '  or,  3  x  =  50,000 


=  50,000  X  1.091  =  54,500,  and  finally, 

KA    CQA 

x  =  ^_£^  =  18,167,  or  about  18,200  cu.  ft.  per  min.     Ans. 
o 

EXAMPLE  4.  —  For  the  same  power  applied  to  each,  what  is  the  rela- 
tive length  of  two  airways  that  will  pass  the  same  quantity  of  air,  the 
first  airway  being  6  ft.  X  6  ft.,  and  the  second  airway  6  ft.  X  8  ft.? 

SOLUTION.  —  The  perimeter  of  the  first  airway  is  2(6  +  6)  =  24  ft., 
and  that  of  the  second  airway  2(6  +  8)  =  28  ft.;  the  area  of  the  first 
airway  is  6  X  6  =  36  sq.  ft.,  and  that  of  the  second  airway  6  X  8  =  48 
sq.  ft.  The  power  and  the  quantity  being  the  same  in  each  case, 
their  ratios  are  each  1,  and  substituting  the  given  values  in  the  general 
expression,  Art.  49,  and  calling  the  length  of  the  first  airway  1,000  ft., 

x         28  /        36\  3 
and  that  of  the  second  airways,  there  is  obtained  ,  1  =  ^-f^.  X  ^7  (  1  X  T^  )  • 

1,UUU         £&  \  *TO/ 

Canceling  the  common  factors, 

<«*  =128,000 


and,  finally,  x  =  —gr^  =  say  2,000  ft.  Hence,  the  length  of  an  air- 
way 6  ft.  X  8  ft.  must  be  practically  double  that  of  an  airway  6  ft.  square, 
in  order  to  pass  the  same  quantity  of  air  under  the  same  power.  Ans. 

50.  If  the  problem  contains  factors  not  included  in  the 
general  expression  given  in  Art.  49,  the  equivalent  factors,  as 
given  by  other  formulas,  may  be  substituted  for  both  airways 
as  was  explained  for  a  single  airway  in  Art.  37.  For  example, 

instead  of  — ,  the  equivalent  values  —  X  ^^.^  may  be  sub- 
iiy  h*       oo,000 

stituted.     This  reduces  to  — ;  therefore,. 
h, 

^i^x-'Xl^X^ 


EXAMPLE  1.  —  If  10  horsepower  produces  a  circulation  of  50,000  cubic 
feet  of  air  per  minute  in  a  certain  mine,  what  power  will  be  required 
to  increase  the  circulation  to  90,000  cubic  feet  per  minute? 

SOLUTION.  —  In  this  case,  all  the  elements  of  the  airway  —  the  length, 
perimeter,  and  area—  are  the  same  in  each  airway  and  their  ratios  are  1; 
hence,  calling  the  required  power  x,  and  substituting  the  given  values 
in  the  general  expression  as  given  above, 

x        /9\s       729 
°rIO=     5       -125 


and,  finally,  x  =  10  X  HI  =  58.32  H.  P.    Ans. 


60  MINE  VENTILATION  §13 

EXAMPLE  2. — If  60  horsepower  will  circulate  40,000  cubic  feet  of  air 
in  an  airway  6  ft.  X  8  ft.  and  6,000  feet  long,  what  horsepower  will  be 
required  to  circulate  50,000  cubic  feet  of  air  in  an  airway  6  ft.  X  10  ft. 
and  4,000  feet  long? 

SOLUTION.— Call  the  required  horsepower  x  and  write  the  values 
given  for  the  power  and  quantity  of  air  in  circulation  and  the  length, 
perimeter,  and  area  of  this  airway  as  follows: 

HORSEPOWER     LENGTH    PERIMETER      QUANTITY     .AREA 
First  airway  .    .  60  6,000  28  40,000  48 

Second  airway  .  x  4,000  32  50,000  60 

x       4,000     32/50,000     48\  s     , 
'  60  =  6^00  X  28  (4^000  X  60J    '    Cancelmg the  coramon  f actors' 


x  =  60  X  if  =  45.7+  H.  P.     Ans. 

EXAMPLE  3.  —  If  the  circulation  of  36,000  cubic  feet  of  air  in  an  air- 
way 6  ft.  X  10  ft.  and  5,000  feet  long  requires  10.9  horsepower,  what 
quantity  of  air  will  16.35  horsepower  circulate  in  an  airway  8  feet 
square,  8,000  feet  long? 

SOLUTION.—  Call  the  required  quantity  of  air  x,  and  write  the  given 
values  for  the  power,  quantity  of  air  and  the  length,  perimeter  and 
area  of  each  of  the  airways,  as  follows: 

HORSEPOWER    LENGTH    PERIMETER    QUANTITY    AREA 


First  airway 

.  10.9 

5,000 

32 

36,000 

60 

Second  airway 

.  16.35 

8,000 

32 

A 

64 

Substituting  these  values, 

16.35 
10.9 

8,000      32  / 
5,000      32  \ 

)X 

(>0\ 
Ml 

". 

Then 

, 

canceling 

the 

common 

3 

factors,    - 

„,§/_£_ 

5  \36.000 

V15\ 
X16/ 

.     Multiplying 

both  members  of  this  equation  by  f  , 


5 


8/*          15\>        16       /_ 
5  \36,000      16/   '        16       \2,4 


28        85  \36,000      16/   '        16       \2,400  X  16/ 
Then,  extracting  the  cube  root  of  both  members  of  this  equation, 

\16  =  38^400'   and>    finallv>  •*"  =  38,400  ^375   =  37,582,   or    about 


38400 
37,600  cu.  ft.  per  min.     Ans. 


PRESSURE 

51.     General   Pressure  Ratio.  —  In   a   similar  way,  as 
before,  when  considering  power,  it  may  be  shown  from  the 

general  formula  p 
hence, 


§13  MINE  VENTILATION  61 

This  expression  is  the  general  expression  for  comparing 
the  pressures  producing  the  circulations  in  any  two  airways. 
It  shows  that  in  every  case  the  pressure  ratio  is  equal  to  the 
continued  product  of  the  lengtJi  ratio,  perimeter  ratio,  the  cube 
of  the  inverse  area  ratio,  and  the  square  of  the  quantity  ratio. 
As  before,  with  respect  to  power,  each  of  these  ratios  acts 
separately,  and  the  value  of  any  one  of  them  may  become  1 
if  the  value  of  that  factor  is  the  same  in  each  airway.  For 
instance,  if  two  airways  have  equal  areas  and  perimeters  and 
pass  the  same  quantity  of  air  —  =  1,  —  =  l.and—  =  1,  and  hence 


that  is,  the  Pressure  ratio  equals  the  length  ratio. 
Similarly,  if  /,  =  /2,  0,  =  o3  and  g1  =  g,, 

h  =  M-       (2) 

A         \aj 

that  is,  the  pressure  ratio  equals  the  cube  of  the  inverse  area  ratio 
for  equal  quantities. 

And  if  /!  =  /2,  0i  =  02,  and  a,  =  a,, 

£  =  H°          (3) 
A      W 

that  is,  the  pressure  ratio  equals  the  square  of  the  quantity  ratio. 

From  the  formula  p  =  *1™-, 
a 

p,  _  k  /,  <?.  z>.'  .  kl,o,  v,'  _  /x      o, 

—   "7"  "^     " 

p*  a^  a,  /a       o, 

then,  if  /t  =  /„  ol  =  oa,  and  a,  =  a,, 


that  is,  the  pressure  ratio  equals  the  square  of  the  velocity  ratio. 
If  /,  =  /„,  0!  =  o,,  and  vl  =  v,, 

^  =  ^  (5) 

A      a. 

that  is,  the  pressure  ratio  equals  the  inverse  area  ratio. 

EXAMPLE  1.—  If  an  airway  4  ft.  X  12  ft.,  and  6,000  feet  long,  is 
passing  a  certain  quantity  of  air  under  a  pressure  of  10  pounds  per 
square  foot,  what  pressure  will  be  required  to  pass  the  same  quantity 
of  air  in  an  airway  6  ft.  X  8  ft.,  and  10,000  feet  long? 


62  MINE  VENTILATION  §13 

SOLUTION.— The  perimeter  of  the  first  airway  is  2(4  +  12)  =  32  ft., 
and  that  of  the  second  airway  2(6  +  8)  =  28  ft.;  the  area  of  the  first 
airway  is  4  X  12  =  48  sq.  ft.,  and  that  of  the  second  airway  6X8 
=  48  sq.  ft.  Here,  the  quantity  of  air  being  the  same  in  each  case, 
the  quantity  ratio  is  1,  and  calling  the  required  unit  of  ventilating 
pressure  x  and  substituting  the  given  values  in  the  general  expression 
for  the  pressure  ratio, 

PRESSURE  LENGTH  PERIMETER  AREA  QUANTITY 
x_  10.000  28          /48\' 

10     "        6,000  32          \48/ 

Canceling  the  common  factors,  -—  =  =  X  5;  and,  finally, 
1U       6      o 

x  =  10  X  If  =  H.6  Ib.  per  sq.  ft.     Ans. 

EXAMPLE  2. — If  a  certain  pressure  is  circulating  10,000  cubic  feet  of 
air  per  minute  in  an  airway  4  ft.  X  12  ft.  and  6,000  feet  long,  what 
quantity  will  the  same  pressure  circulate  in  an  airway  6  ft.  X  8  ft. 
and  10,000  feet  long? 

SOLUTION. — The  airways  being  the  same  as  in  the  previous  example, 
the  perimeters  and  areas  are  the  same.  In  this  case,  the  pressure 
ratio  is  1,  and  calling  the  required  quantity  of  air  x  and  substituting 
the  given  values  in  the  formula, 

_  10,000      28  /48\  3  /    x     \  * 
~   6,000  X  32  \48/    \10,000/ 
Canceling  the  common  factors, 


38  \10,000/          24  \10,000/ 
Multiplyin'g  both  members  of  this  equation  by  f£ , 

24       24      35  /     x    \"  i 

35  =  35  X  24(ro7)0o)    'or'6857  = 
Extracting    the    square   root   of   both    members    of  this   equation, 


x  =  10,OOOV.6857  =  8,280,  or  about  8,300  cu.  ft.  per  min.     Ans. 

EXAMPLE  3. — If  it  is  necessary  to  double  the  amount  of  air  in  a 
mine  or  airway:  (a)  in  what  proportion  should  the  pressure  be 
increased?  (b)  in  what  proportion  should  the  power  be  increased? 

SOLUTION. —  (a)  Here,  the  length,  perimeter,  and  area  are  constant, 
and  their  ratios  each  1.  Since  the  quantity  of  air  is  to  be  doubled, 

2 
the  quantity  ratio  is  y.     Now,  calling  the  original  pressure  1  and  the 

required  pressure  x,  and  substituting  the  given  values  in  formula  2, 
Z  =  /?\  *;  or,  x  =  2'  =  4.    Ans. 


§13  MINE  VENTILATION  63 

That  is  to  say,  the  pressure  required  to  double  the  quantity  of  air 
in  circulation  is  four  times  the  original  pressure. 

(6)  As  before,  the  length,  perimeter,  and  area  being  the  same, 
these  ratios  are  1  and  the  quantity  ratio  is  2.  Hence,  calling  the 
original  power  1  and  the  required  powers,  and  substituting  the  given 
values  in  the  expression  for  power,  Art.  48,  or  in  the  general  expres- 
sion for  power,  Art.  49, 

*  =  1  X  1  (2  X  I)3;  or,  x  =  23  =  8.     Ans. 

That  is  to  say,  the  power  required  to  double  the  quantity  of  air  in 
circulation  is  eight  times  the  original  power. 

EXAMPLE  4. — If  a  given  pressure  per  square  foot  will  circulate  40,000 
cubic  feet  of  air  in  an  airway  9  ft.  X  6  ft.,  what  should  be  the  length  of 
a  side  of  a  square  airway  that  will  pass  70,000  cubic  feet  of  air  under 
the  same  pressure,  the  length  of  both  airways  being  the  same? 

SOLUTION.— Here,  the  pressure  and  the  length  of  the  airway  are  the 
same  in  each  case  and  their  ratios  1.  The  perimeter  of  the  first  air- 
way is  2(9  +  6)  =  30  ft.  and  its  area  9  X  6  =  54  sq.  ft.  Calling  the 
required  length  of  one  side  of  the  square  airways,  its  perimeter  is  4  x 
and  its  area  x* .  Substituting  these  values  in  the  expression  for  pressure, 


30  Vr7    \40,000y 

Canceling  the  common  factors,   1  =  •srl — 5)    (T)   •     In    order   to 

6(J  \x  /     \4/ 

simplify  the  operation  as  far  as  possible,  the  last  equation  above  may 


be  written  as  follows: 

54  54  54 


xXx 
Then,  x*  =  64,298;   and, 

x  -  </64,298  =  9.15,  say  9  ft.     Ans. 

EXAMPLE  5.  —  If  a  water  gauge  of  1.5  inches  produces  95,000  cubic 
feet  of  air  in  a  certain  airway,  what  quantity  will  a  2-inch  water  gauge 
produce  in  the  same  mine? 

SOLUTION.  —  Here,  the  mine  being  the  same  in  each  case,  the  length, 
perimeter,  and  area  ratios  are  each  1,  ~  =  I  --J  ;  since  p  =  5.2  t, 

£i  =  '^L*!  =  *';  hence,-  =  (?-}'.      Therefore,   calling   the   required 
/>a       0.2/,       *2  *2        \qt) 

quantity  x, 

2_  =  (_*_\  *.         4  =  (_*_\  * 
1.5  "  \95,000/   '  °r'  3  ~  \95,000/ 

Extracting  the  square  root  of  both  members,  Vl.33  =  55-757^;  and, 

.fO,UUU 

finally, 
x  =  95,000  VT33  =  109,687,  or  about  109,700  cu.  ft.  per  min.     Ans. 

145—15 


Hi  MINE  VENTILATION  §13 

EXAMPLE  6. — If  36,000  cubic  feet  of  air  is  passing  in  an  airway 
lift.  X  10  ft.,  under  a  pressure  of  3.6  pounds  per  square  foot,  what 
pressure  will  be  required  to  pass  the  same  quantity  of  air  through 
an  airway  5  ft.  +  10  ft.  of  the  same  length? 

SOLUTION.— The  perimeter  of  the  first  airway  is  2(6  +  10)  =  32  ft., 
and  the  area  6  X  10  =  60  sq.  ft.;  the  perimeter  of  the  second  airway  is 
2(5 +  10)  =30  ft.,  and  the  area  5  X  10  =  50  sq.ft.  The  length  ratio  and 
the  quantity  ratio  are  each  1.  Hence,  calling  the  required  pressure  x, 

^  =  1X™(™)    X  I2.     Then,   canceling    the    common    factors,  -*• 

O.D  o^  \OU/  o.O 

15  /6\  3 

=  i6W  ;  and>finally' 

x  =  3.6  X  ft  X  fM  =  5.8  Ib.  per  sq.  ft.     Ans. 


EXAMPLES    FOR    PRACTICE 

1.  If  you  jhave  two  airways  under  the  same  pressure,  one  6  feet 
wide,  6  feet  high,  and  5,000  feet  long,  the  other  8  feet  wide,  4^  feet 
high,  and  5,000  feet  long,  which  will  pass  the  greater  quantity  of 
air,  and  why? 

Ans.  The  first  airway;  because  it  has  less  rubbing  surface  for  the 
same  area  of  cross-section. 

"2.  With  a  water  gauge  of  ^  inch,  the  quantity  of  air  passing  is 
24,000  cubic  feet  per  minute;  what  water  gauge  will  be  required  to 
pass  36,000  cubic  feet  per  minute?  Ans.  1.35  in. 

3.  If  16,500  cubic  feet  of  air  is  passing  per  minute  with  a  pressure 
of  4.68  pounds  per  square  foot,  what  quantity  will  pass  with  a  pressure 
of  6.24  pounds  per  square  foot? 

Ans.  19,052,  or  about  19,000,  cu.  ft.  per  min. 

4.  If  3  horsepower  passes  15,000  cubic  feet  of  air  per  minute,  what 
horsepower  will  be  required  to  double  the  quantity  in  the  same  airway? 

Ans.  24  H.  P. 

5.  If  32,000  cubic  feet  of  air  is  passing  through  an  airway  6  ft.  X  5  ft. , 
under  a  pressure  of  3.6  pounds  per  square  foot,  what  pressure  is  neces- 
sary in  an  airway  9  ft.  X  5  ft.  to  pass  the  same  quantity,  both  airways 
being  of  the  same  length?  Ans.  1.3575  Ib.  per  sq.  ft. 

6.  If  a  pressure  of  3.2  pounds  per  square  foot  produces  a  velocity 
of  560  feet  per  minute,  what  pressure  is  required  to  produce  a  velocity 
of  700  feet  per  minute  in  the  same  airway?  Ans.  5  Ib.  per  sq.  ft. 

7.  If  24,000  cubic  feet    is    passing  through   an   airway   having  a 
rubbing  surface  of  75,000  square  feet,  what  quantity  will  the  same 
pressure  pass  if  the  rubbing  surface  is  increased  to  100,000  square  feet, 


§13  MINE  VENTILATION  65 

the  increase  of  rubbing  surface  being  due  to  the  lengthening  of  the 
airway?  Ans.  20,785,  or,  about  21,000  cu.  ft. 

8.  If  in  an  airway  1,200  feet  long  the  air  has  a  velocity  of  400  feet 
per  minute  under  a  pressure  of  3  pounds  per  square  foot,  what  must 
the  pressure  be  to  maintain  the  same  velocity  if  the  length  of  airway 
is  increased  to  1,800  feet?  Ans.  4.5  Ib.  per  sq.  ft. 

9.  If  the  air  passes  with  a  velocity  of  600  feet  per  minute  through 
an  airway  whose  sectional  area  is  64  square  feet,  what  will  the  velocity 
be  for  an  area  of  48  square  feet,  the  pressure  and  the  rubbing  surface 
remaining  the  name?  Ans.  520  ft.  per  min. 

10.  Two  circular  airways  of  the  same  length  have  diameters  of 
3  feet  and  4  feet,  respectively;  if  a  pressure  of  5  pounds  per  square 
foot  will  force  the  air  through  the  4-foot  airway,   what  pressure  is 
required  to  pass  the  same  quantity  through  the  3-foot  airway? 

•    Ans.  21.07  Ib.  per  sq.  ft. 

11.  If  10,000  cubic  feet  of  air  passes  per  minute  through  a  circular 
airway  12  feet  in  diameter,  how  many  cubic  feet  per  minute  will  pass 
through  an  airway  6  feet  in  diameter  and  having  the  same  length,  the 
pressure  being  the  same  in  both  cases? 

Ans.  1,768  cu.  ft.  per  min.,  or,  say  1,800  cu.  ft. 

12.  If  40,000  cubic  feet  of  air  is  circulated  in  an  airway  6  ft.  X  8  ft. 
by  a  certain  power,  what  quantity  of  air  will  the  same  power  circulate 
in  an  airway  8  ft.  X  12  ft.  of  the  same  length? 

Ans.  71,032,  or  71,000  cu.  ft.  per  min. 


CHOICE  OF  AIRWAYS 

52.  Aside  from  other  questions  that  may  determine  the 
form  of  airway  best  adapted  to  any  given  case,  the  econom- 
ical ventilation  of  the  mine  requires  that  form  of  airway  that 
will  pass  the  largest  quantity  of  air  with  the  least  expendi- 
ture of  power.  That  is,  the  ratio  of  the  quantity  of  air  in 
circulation  to  the  cube  root  of  the  power  should  be  a  maxi- 
mum. Hence,  in  deciding  between  two  or  more  forms  of  air- 
way that  should  be  adopted,  as  far  as  ventilation  is  concerned, 
that  offers  the  least  resistance  to  the  passage  of  the  air. 

EXAMPLE  1. — Which  9f  two  airways  of  equal  length  will  pass  the 
larger  quantity  of  air  with  the  same  expenditure  of  power,  if  one  is 
4  ft.  X  16  ft.  and  the  other  is  8  ft.  X  8  ft? 

SOLUTION. — The  area  of  these  airways  is  the  same;  the  perimeter  of  the 
first  airway  is  2(4  +  16)  =  40  ft.  and  that  of  the  second  2(8  +  8)  =  32  ft. 


66  MINE  VENTILATION  §13 

The  formula  for  the  quantity  of  air  passing  through  an  airway  is 

«  =  — ~-,  or  q  =  a\/ry->  tnen  if  ?i  is  tne  quantity  passing  through 

the  first  airway  and  qt  the  quantity  passing  through  the  second  air- 
way, the  relative  amounts  passing  through  the  two  airways  when  the 
powers,  lengths,  and  areas  are  the  same  are  given  by  the  expression 


"A/*77, 

or,  canceling  common  factors,  —  =  \/— ,  and  substituting  the  values  for 
o,  and  oa,  then  £?  =  V/??  =  V/l  =  tfs  =  .928,  or  ?,  =  .928  q,;  that  is, 


for  1,000  cu.  ft.  of  air  passing  through  the  second  airway,  928  cu.  ft. 
will  pass  through  the  first  airway.  Ans. 

EXAMPLE  2.— If  you  had  your  choice  of  the  following  intake  air- 
ways, which  would  you  prefer  and  why,  all  the  airways  being  of  the 
same  length?  The  first  airway  is  10  ft.  X  10  ft.;  the  second,  5  ft. 
X  20  ft.;  the  third  circulation  includes  two  airways  each  5  ft.  X  10  ft. 

SOLUTION. — The  perimeters  and  areas  in  each  case  are  as  follows: 

First  circulation,  perimeter  2(10  +  10)  =  40  ft.;  area  10  X  10 
=  100  sq.  ft. 

Second  circulation,  perimeter  2(5  +  20)  =  50  ft.;  area  5  X  20 
=  100  sq.  ft. 

Third  circulation,  perimeter  2  X  2(5  +  10)  =  60  ft.;  area  2  X  5  X  10 
=  100  sq.  ft. 

Using  the  same  formula  as  in  Example  1,  q  =  #  \fr-i — 

If  ^,  is  the  quantity  of  air  passing  in  the  first  airway;  gt,  the  quantity 
of  air  passing  in  the  second  airway;  <?3,  the  quantity  of  air  passing  in  the 
third  airway;  since  a,  u,  kt  and  /  are  the  same  for  all  the  airways,, they 

will  cancel  and  ?-*  =  ^  =  yjj^  =  "O  =  .928.     Similarly  q-  =  ^ 

=  ^1.666  =  .873.  That  is  to  say,  if  the  same  power  be  applied  to  each 
airway,  for  every  1,000  cubic  feet  of  air  passing  in  the  first  mine, 
there  will  be  928  cu.  ft.  in  the  second,  and  873  cu.  ft.  in  the  third. 
The  last  circulation,  or  the  third  mine,  includes  two  airways  each 
having  the  same  length  as  the  airwa'ys  in  the  first  and  second  mines. 
The  first  airway  is,  therefore,  the  most  economical  form  to  adopt. 

Ans 


§13  MINE  VENTILATION  67 


COMPARING    SIMILAR   AIRWAYS 

53.  Although  similar  airways  may  be  compared  in  the 
same  manner  as  any  other  airways  using  the  methods  pre- 
viously described,  it  is  often  desired  to  compare  circulations 
for  such  airways  without  reference  to  either  the  perimeter  or 
the  area  of  the  airways,  but  by  basing  the  comparison  on  the 
length  of    any  corresponding    sides   or   dimensions  of   the 
aifways.     When  comparing  the  circulation  of  air  in  these 
airways,  the  perimeter  o  and  the  area  a  of  the  airway  may  be 
omitted,  substituting  instead  the  diameter  of  the  circle  or 
side  of  a  square,  a  side  or  the  altitude  of  a  triangle  or  trape- 
zoid,  or  any  other  corresponding  dimension.    In  such  a  case, 
the  corresponding   dimension,   whether   the   diameter  of  a 
circle    or   the    side  of   a  square,   triangle,  or    trapezoid,  is 
denoted  by  the  same  symbol  d  with  a  small  subscript  figure 
i,  3,  3,  etc.,  to  indicate  the  airway  to  which  it  belongs. 

It  is  proved  in  geometry  that  the  areas  of  similar  figures 
are  to  each  other  as  the  squares  of  any  corresponding  side,  the 
squares  of  their  perimeters,  or  the  squares  of  any  line  similarly 
placed  in  them,  as,  for  example,  a  diagonal  or  diameter. 

54.  General    Power    Ratio    for    Similar    Airways. 

By  substituting  in  the  general  power  ratio  given  in  Art.  49, 

f  for  '•  and  (£Y  for  (*)',  S  i  4  X  *  X  j '.  X  (*)';  hence, 

d,         oa          VfcV          \aj     u,       !,      d,      d,e      \qj 

by  cancelation,  *  ..  4  (AV  (fcY 

«2       /„  \dj    \qj 

This  is  the  general  expression  for  comparing  the  powers 
producing  the  circulations  in  any  two  similar  airways;  it 
shows  that  in  every  case  the  power  ratio  is  equal  to  the  con- 
tinued product  of  the  length  ratio,  the  fifth  power  of  the  inverse 
diameter  or  side  ratio,  and  the  cube  of  the  quantity  ratio. 

55.  General  Pressure  Ratio  for  Similar  Airways. 

In  like  manner,  by  substituting  these  values  in  the  general 
pressure  ratio  given  in  Art.  51,  and  reducing  as  before  by 

cancelation,  *  - 


68  MINE  VENTILATION  §13 

This  is  the  general  expression  for  comparing  the  pressures 
producing  the  circulation  in  any  two  similar  airways,  and  it 
shows  that  in  every  case,  the  pressure  ratio  is  equal  to  the  con- 
tinued product  of  the  length  ratio,  the  fifth  power  of  the  inverse 
diameter  or  side  ratio,  and  the  square  of  the  quantity  ratio.  A 
few  examples  will  show  the  use  of  these  formulas. 

EXAMPLE  1.  —  In  a  certain  mine,  20,000  cubic  feet  of  air  is  passing 
in  an  airway  6  ft.  X  8  ft.  It  is  proposed  to  enlarge  this  airway  in 
the  same  rectangular  form  so  as  to  circulate  60,000  cubic  feet  of  air 
with  the  same  power.  What  will  be  the  dimensions  of  the  airway  to 
accomplish  this  purpose? 

SOLUTION.  —  The  power  and  the  length  of  the  airways  being  the 
same  in  each  case,  their  ratios  are  each  1.  Calling  the  ratio  of  any 
side  of  the  new  airway  to  the  corresponding  side  of  the  old  airway  x, 
and  substituting  the  given  values  in  the  general  power  ratio  given  in 

Art.  54,  1  =  1  X  Xs  (^  —  j   .     Canceling  the  common  factors, 

1  =  x*  (jj  a=  |°;  or  xs  =  9;  and  x  =  jfc  =  1.55 

Hence,  the  length  of  any  side  in  the  new  airway  is  1.55  times  the 
length  of  the  corresponding   side  in  the  old  airway;   therefore,   the 
height  of  the  new  airway  is  1.55  X  6  =  9.3  ft.     Ans. 
Width  of  new  airway  is  1.55  X  8  =  12.4  ft.     Ans. 

EXAMPLE  2.  —  If  a  given  pressure  circulates  20,000  cubic  feet  of  air 
in  an  airway  10  feet  in  diameter,  how  many  cubic  feet  of  air  will  the 
same  pressure  circulate  in  an  airway  6  feet  in  diameter,  each  airway 
having  the  same  length? 

SOLUTION.—  The  pressure  and  the  length  of  the  airway  being  the 
same  in  each  case,  these  ratios  are  each  1.  Calling  the  required 
quantity  of  air  x,  and  substituting  the  given  values  in  the  general  pres- 

(10\  *  t     x    \  * 
ft)    (yo  onn)  '    Canceling  the 

common  factors, 

5 


5W     *    V=3.125/     x    \- 
3/    ^20,0007         243    \20,000/ 


•  243 

Multiplying     both     members     of    this     equation     by    „  ..__    gives 

243          243        3,125  /     x    \  *  243        /    x     \  * 

37125  =  3^25  X  "243"  (mjOOo)   '  °r  3J25  =  (26^60)   '     N° 
the  second  member  of  the  equation  first  and  extracting  the  square  root 

„  /     »>  1  •  > 

of  each  member,  ~~  =\/qT^  =  ^-0777  =  .278;  and,  finally, 

ZU  ,  UUU          \  o  ,  1  ^O 

x  =  20,000  X  .278  =  5,600  cu.  ft.  per  min.    Ans. 


MINE  VENTILATION 

(PART  2) 


SPLITTING  AIK-CURRENTS 


GENERAL    PRINCIPLES 

1.  When  a  mine  is  first  opened,  the  air  is  conducted  in  a 
single  current  throughout  the  mine.  As  the  development  of 
the  mine  advances,  the  distance  the  air  must  travel  increases 
rapidly,  and  it  may  be  assumed  that  the  rubbing  surface 
increases  approximately  in  the'  same  proportion.  If  the 
power  producing  the  circulation  of  air  remains  constant,  an 
increase  of  rubbing  surface  produces  a  decrease  in  velocity, 
as  is  shown  by  the  formula, 

u  —  ksv* 

For  example,  suppose  that  the  rubbing  surface  s  in  a 
certain  mine  is  100,000  square  feet  and  that  the  veloc- 
ity v  is  600  feet  per  minute;  the  power  on  the  air  is  then 
u  =  .00000002  X  100,000  X  600s  =  432,000  foot-pounds  per 
minute. 

With  the  same  power  applied  to  the  air,  increasing  the 
rubbing  surface  eight  times  will  decrease  the  velocity  one- 
half,  as  is  shown  in  the  following  equation,  u  =  .00000002 
X  800,000  X  300s  =  432,000  foot-pounds.  That  is,  as  was 
shown  in  Mine  Ventilation,  Part  1.  For  the  same  power  applied, 
the  velocity  varies  inversely  as-  the  cube  root  of  the  rubbing 
surface. 

This  explanation  also  shows  that  the  application  of  a  cer- 
tain power  against  a  certain  rubbing  surface  produces  a  certain 

Copyrighted  by  International  Textbook  Company.    Entered  at  Stationers'  Hall,  London 


2  MINE  VENTILATION  §14 

velocity  in  the  mine  or  airway,  regardless  of  the  sectional 
area  of  the  airway.  Advantage  is  taken  of  this  fact  to 
increase  the  quantity  of  air  circulated  in  a  mine  or  airway  by 
a  given  power,  by  increasing  the  sectional  area,  or,  the  area 
of  passage  of  the  air  through  the  mine.  In  order  to  do  this 
without  increasing  the  rubbing  surface  in  the  mine,  it  is  neces- 
sary to  divide  the  air-current  into  two  or  more  currents,  each 
of  which  is  called  an  air  split.  Dividing  a  single  air-current 
into  two  or  more  currents  is  called  splitting  the  air-current, 
or  splitting  the  air.  For  example,  it  may  be  possible  to 
divide  an  airway  12,000  feet  long  into  two  airways  each 
6,000  feet  long  or  three  airways  each  4,000  feet  long.  By 
doing  this,  the  rubbing  surface  remains  unchanged,  but  the 
sectional  area  or  the  area  of  passage  for  the  air  through 
the  mine  is  increased  two,  three,  etc.  times,  according  to  the 
number  of  separate  airways,  because  there  are  two  or  three, 
or  more,  shorter  passageways  instead  of  one  long  airway. 
This  is  on  the  same  principle  that  three  4-inch  pipes  each 
5  feet  long  will  discharge  more  water  from  a  tank  than  one 
4-inch  pipe  15  feet  long. 

2.  Effect  of  Splitting  the  Air.— If  the  total  rubbing 
surface  of  the  several  airways  is  the  same  as  that  of  the 
single  airway,  the  application  of  the  same  power  will  pro- 
duce the  same  velocity  in  each  of  the  two  or  three  airways 
as  was  formerly  produced  in  the  single  airway;  then,  since 
q  =  a  v  and  since  a  and  v  are  the  same  for  each  airway  as 
for  the  single  airway,  it  is  evident  that  by  thus  splitting  the 
air  the  total  quantity  of  air  circulating  through  the  mine  is 
increased  two,  three,  etc.  times,  according  to  the  number  of 
airways.  This,  however,  is  a  theoretical  case,  inasmuch  as 
it  is  not  generally  possible  to  divide  the  entire  air-current  at 
the  mouth  of  the  mine  into  two  or  more  currents,  but  the 
circulation  in  the  mine  will  always  consist  of  a  single  main 
intake  from  which  the  several  air  splits  are  taken.  The 
several  splits  usually  unite  to  form  a  single  return.  For 
this  reason,  the  power  on  the  air  becomes  less  just  after  the 
split  is  made,  owing  to  the  greater  consumption  of  power 


§14  MINE  VENTILATION  3 

by  the  increased  quantity  of  air  that  must  pass  through  the 
single  main  airway  before  the  point  of  splitting  is  reached. 
Splitting  the  air  at  any  point  in  the  mine  causes  a  fall  of 
pressure  at  that  point,  because  there  are  then  two  or  more 
avenues  of  escape  for  the  air  instead  of  one.  The  power  on 
the  air  at  the  mouth  of  the  mine  remaining  constant,  any 
relief  or  fall  of  pressure  in  the  mine  causes  an  increased 
quantity  of  air  to  pass  into  and  through  the  mine.  Since 
this  increased  quantity  must  all  pass  through  the  main  air- 
way, before  reaching  the  point  of  split,  there  is  evidently  an 
increase  of  the  power  consumed  in  the  main  airway,  and,  as 
a  result,  there  is  less  power  on  the  air  at  the  mouth  of  the 
splits. 

For  example,  suppose  that  50,000  cubic  feet  of  air  is  cir- 
culated in  a  single  current  in.  a  mine  by  10  horsepower  and 
that  2  horsepower  is  consumed  in  the  shaft  and  main  intake 
airway  before  the  air  reaches  the  point  where  it  is  to  be 
divided.  The  power  on  the  air  at  this  point  is  then  10  —  2 
=  8  horsepower.  When  the  split  is  made,  a  larger  quantity 
of  air  will  pass  into  the  mine,  and  the  velocity  of  the  air- 
current  and,  consequently,  the  resistance  in  the  shaft  and  the 
main  intake  airway  is  very  much  increased,  and  the  power 
now  consumed  in  the  shaft  and  main  intake  airway  may  be 
6  horsepower  instead  of  2  horsepower,  leaving  only  10—6 
=  4  horsepower  on  the  air  at  the  mouth  of  the  splits. 
Although  the  quantity  of  air  in  circulation  would  be  doubled 
by  dividing  the  current  into  two  splits,  if  the  power  on  the 
air  remained  constant  at  this  point,  the  effect  of  splitting  is 
reduced  because  the  power  on  the  air  at  the  mouth  of  the 
splits  is  one-half  the  original  power  at  this  point.  But,  in 
any  circulation,  the  quantity  of  air  varies  as  the  cube  root  of 
the  power  producing  that  circulation;  hence,  the  power  being 
one-half,  the  quantity  will  be  on  this  account,  A/.5  =  .79,  or 
about  four-fifths  of  the  original  quantity.  The  combined 
effect  of  splitting  the  air,  in  this  case,  is,  therefore,  2  X  i 
=  If.  That  is  to  say,  the  effect  of  splitting  the  air-current 
at  this  point  in  the  mine  will  be  to  increase  the  entire  cir- 
culation in  the  mine  three-fifths  of  the  original  quantity. 


MINE  VENTILATION 


§14 


producing  1|  X  50,000  =  80,000  cubic  feet  of  air  by  the  same 
power  applied  at  the  mouth  of  the  mine. 

The  following  three  examples  show  the  effect  of  splitting 
the  air-current.  In  the  first  example,  the  power  required  to 
circulate  a  given  quantity  of  air  in  a  continuous  current  is 
calculated.  In  the  second  example,  the  power  required  to 
circulate  the  same  quantity  of  air  through  the  same  length 
of  airways  in  four  splits  is  calculated;  this  includes  the 
power  absorbed  by  the  two  shafts.  In  the  third  example, 
the  quantity  of  air  that  will  be  circulated  by  the  original 

power  in  four  splits 
is  found,  the  size  and 
length  of  airways 
being  the  same  in  all 
the  examples. 


EXAMPLE  1.— Find 
the  power  that  will  cir- 
culate 24,000  cubic  feet 
of  air  per  minute  under 
the  following  conditions: 
The  air  to  be  circulated 
through  the  mine  in  one 
continuous  current  16,000 
feet  long  including  the 
length  of  the  return  air- 
way and  the  depths  of 
the  downcast  and  up- 
cast shafts  The  size  of 
all  the  airways  and  shafts  is  to  be  6  ft.  X  10  ft. 

SOLUTION. — The  perimeter  of  airways  and  shaft  is  o  =  2(6  +  10) 
=  32  ft.,   and  the  area  6  X  10  =  60  sq.   ft.     Substituting   the  given 

values  in  the  formula  for  power,  «  =  33,000  h  =  ^-  and  dividing 

by  33,000  to  obtain  the  horsepower, 

kloq*    _  .00000002  X  16,000  X  32  X  24, OOP3 
33,000 a3  33,000  X603 


19.859  H.  P.    Ans. 


EXAMPLE  2.— Find  the  power  that  will  circulate  24,000  cubic  feet  of 
air  through  a  mine  under  the  following  conditions:  The  air  is  divided 
at  the  foot  of  the  downcast  d,  Fig.  1,  into  four  splits,  each  3,600  feet 
long  and  6  ft.  X  10  ft.  in  section,  and  is  finally  united  at  the  foot  of 
the  upcast  u.  The  shafts  are  each  800  feet  deep  and  are  also 


§14  MINE  VENTILATION  5 

6  ft.  X  10  ft.  in  section.     It  will  be  noticed,  that  the  size  and  total 
length  of  airways  and  shafts  are  the  same  as  in  example  1. 

SOLUTION.  —  It  is  evident  that  the  total  power  producing  the  cir- 
culation is  equal  to  the  sum  of  the  powers  absorbed  in  the  two  shafts 
and  in  the  four  splits  in  the  mine.  Since  the  size  of  each  shaft  is 
equal  to  the  size  of  the  airways,  the  two  shafts  each  800  ft.  deep  may 
be  considered  as  an  airway  1,600  ft.  long.  As  before,  the  perimeter  is 
32  ft.  and  the  area  60  sq.  ft.  Substituting  these  values  in  the  same 
formula  as  in  example  1  to  obtain  the  horsepower, 

.         k  log3    _  .00000002  X  1,600  X  32  X  24,  OOP3  _ 
"  3  ~  33,000  X  60s 


The  horsepower  absorbed  in  passing  the  air  through  four  equal 
splits  is  four  times  the  power  required  for  one  split.     Since  the  area 
and  the  perimeter  are  the  same  as  before,  and  the  length  of  each  split 
is  3,600   ft.,  and  since  the  quantity  of  air  passing  in  each  split  is 
g-4°°°-  =  6,000  cu.  ft.,  the  power  absorbed  in  the  four  splits  is  found 
by  substituting  these  values  in  the  formula  for  the  horsepower, 
,        4(.OOOOOOQ2  X  3,600  X  32  X  6,000s) 
33,000  X  60° 

The  total  power  producing  the  circulation  is,  therefore,  1.986  +  -279 
=  2.265  H.  P.     Ans. 

The  horsepower  in  this  case  is  more  easily  figured  by  comparing 
this  circulation  with  that  in  example  1.     In  the  general  expression  for 

comparing  powers  —  =  -^  X  —  X  —  4  X  —  V    Since  the  dimensions  of 
u,       f2      o,      ga       di 

the  cross-section  of  the  airway  are  the  same  in  each  cast,  and  the 
quantity  of  air  in  circulation  in  the  shafts  is  also  the  same,  the  perime- 

u         I 
ter,  area,  and  quantity  ratios  are  all  1,  and  —  =  -~  .     Then,  calling  the 

#2  *2 

required    horsepower   xt  =  =       !    and  x  =  19-859  X  A 


=  1.986  H.  P.  In  the  same  manner,  the  power  consumed  in  each  of 
the  four  splits  is  found  by  comparing  the  circulation  in  one  split  with 
the  circulation  in  example  1.  In  making  this  comparison,  the  length 


ratio  is  VTT;  =  TTJ.  the  perimeter  and  area  ratios  are  each  1  and  the 


quantity  ratio  is  -;  hence,  substituting  these  values  in  the  same 
general  expression  as  the  preceding  and  multiplying  by  4,  to  obtain 
the  total  power  for  the  four  splits,  and  calling  this  power  x,  ^f 


-  4  x  S>  x  ©  '  =  &>'  and'  flna"y'  *  '      W      -  '279  H-  p'   As 

before,  the  total  power  consumed  in  the  two  shafts  and  the  four  splits 
or  airways  is  1.986  +  .279  =  2.265  H.  P.    Ans.     This  result  shows  that, 


6  MINE  VENTILATION  §14 

in  this  case,  it  required,  after  splitting,  but  11.4  per  cent,  of  the  power 
originally  required  to  pass  the  same  quantity  of  air  through  the  mine. 

EXAMPLE  3. — Find  the  quantity  of  air  that  the  original  power  found 
in  example  1  will  circulate  in  the  four  splits  described  in  example  2, 
all  the  conditions  in  the  mine  being  the  same  as  in  example  2,  except 
that  the  power  at  the  mouth  of  the  mine  is  increased  from  2.265  horse- 
power to  19.859  horsepower. 

SOLUTION. — Since  the  conditions  with  respect  to  the  mine  in  this 
circulation  are  the  same  as  in  example  2,  the  length  ratio,  perimeter 
ratio,  and  area  ratio  of  the  airways  are  all  1  in  the  general  power  ratio, 
and  the  power  ratio  is  equal  to  the  cube  of  the  quantity  ratio.  Hence, 
calling  the  required  quantity  of  air  in  this  case  x,  and  substituting  the 

19.859       /     x    \3 

given  values  in  the  general  power  ratio,  ~^~^^~  —  (04.  nno/   •     Extract- 
ing the  cube  root  of  both  members  of  this  equation  and  writing  the 

1C  ho  k^Q  * 

second  member  of  the  equation  first,  ^QOO  =  \2lJ65"  ~  ^8'767  =  2'062; 
and,  finally, 

x  =  24,000  X  2.062  =  49,488,  say  49,500  cu.  ft.  per  min.     Ans. 
Comparing  the  result  in  example  3  with  the  quantity  circulated  in 
example  1,  it  will  be  seen  that,   by  splitting  as  in  example  2,   over 
twice  as  much  air  is  passed  through  the  mine  with  the  same  power. 

3.  The  practical  effect  of  splitting  the  air-current  is  thus 
seen  to  be  to  increase  the  circulation  of  air  in  the  mine  per 
unit  of  power  applied.  Theoretically,  splitting  the  air-current 
in  the  mine  does  not  decrease  the  mine  resistance,  as  it  does 
not  in  any  way  change  the  rubbing  surface;  the  velocity  of 
the  air-current  would  therefore  not  be  changed  if  it  were  not 
that  the  entire  circulation  must  pass  through  a  single  airway 
for  a  portion  of  the  distance.  On  this  account,  the  velocity 
is  increased  in  the  main  airway,  which  increases  the  power 
consumed  in  that  portion  of  the  mine  and  decreases  the 
power  on  the  air  beyond  the  point  of  splitting.  The  decrease 
of  power  on  the  air  at  the  mouth  of  the  several  splits  causes 
a  decrease  of  velocity  in  the  splits,  the  rubbing  surface 
remaining  constant.  Although  the  resistance  of  the  main 
airway  is  increased  by  the  increased  velocity  at  that  point, 
the  resistance  of  the  splits  is  very  much  decreased  on  account 
of  the  reduced  velocity  in  the  splits,  and  the  net  mine  resist- 
ance is  also  decreased.  The  practical  effect  of  splitting  is, 


§14  MINE  VENTILATION  7 

therefore,  an  increased  quantity  of  air  per  unit  of  horse- 
power, or  a  decrease  of  power  required  for  the  same  quantity 
of  air  in  circulation,  a  decrease  of  mine  resistance,  and  a 
decrease  of  pressure. 

4.  Limit    of    Splitting   Air. — The   practical  limit  of 
splitting  the  air  in  a  mine  is  determined  by  the  velocity  of 
the  air  in  the  several  splits.     Owing  to  the  decrease  of  power 
at  the  mouth  of  the  splits,  each  new  split  made  in  the  mine 
causes  another  decrease  in  the  velocity  of  the  air.     When 
this  velocity  is  too  low  to  sweep  away  the  gases  accumulated 
in  the  workings,  the  limit  of  splitting  in  that  section  of  the 
mine  has  been  reached  and  any  further  increase  of  the  quan- 
tity of  air  in  circulation  must  be  obtained  by  increasing  the 
power  on  the  air,  or  by  scaling  the  air  traveling  in  another 
split. 

The  term  scaling  is  used  to  describe  the  practice  of  rob- 
bing one  air  split  to  supply  another.  A  scale  of  air  is  a 
small  air  split  taken  from  the  main  current  or  from  another 
split  for  a  special  purpose,  as,  for  example,  the  ventilation  of 
the  mine  stables.  It  is  often  possible  to  increase  the  quantity 
of  air  circulating  in  any  section  of  the  mine  by  cleaning  up 
the  falls,  enlarging  the  break-throughs  and  straightening  the 
air-courses,  and  short-circuiting  the  air-current  wherever 
possible,  thus  reducing  the  resistance  in  that  section. 

5.  Advantages    of    Splitting    the    Air. — The    chief 
advantages  of  splitting  the  air-current  in  a  mine  are:     (1)  A 
larger  volume  of  air  may  be  circulated  by  the  same  power, 
or  a  less  power  will  be  required  for  the  same  quantity  of  air 
in  circulation.     (2)   By  this  means,  the  entire  circulation  of 
the  mine  is  divided  into  separate  districts,  and  the  circulation 
in  each    district  can  thus  be  easily  adjusted   to  meet,  the 
requirements.     (3)   Purer  air  is  supplied  to  the  working  face 
throughout  the  mine  since  the  return  air  from  each  district 
is  conducted  directly  into  the  main  return  without  passing 
through    another    district    of    the    mine.     (4)   If    a    small 
explosion  occurs  in  one  district  of  the  mine,  its  effect  is 
often  confined  to  that  district.     (5)  A  large  volume  of  air  is 


8  MINE  VENTILATION  §14 

circulated  in  the  mine  at  a  lower  velocity  than  when  the  air 
is  not  split,  thereby  reducing  the  mine  resistance  and  the 
dangers  arising  from  high  velocities  of  the  air-current  in  a 
gassy  mine. 

6.  Requirements   of    Law   In   Regard   to   Splitting 
the  Air. — Some  of  the  state  mining  laws  require  that  the 
air  circulating  in  a  mine  shall  be  so  divided  or  split  as  to 
give  a  separate  current  of  air  to  each  section  of  the  mine  and 
specify  the  maximum  number  of  men  permitted  to  work 
on  a  single  current  or  split.     The  Anthracite  Mining  Laws 
of    Pennsylvania    specify    that   not   more   than  seventy-five 
persons   shall  be  permitted  to  work  on  a  single  air  split. 
The   Bituminous   Mining    Laws   of   Pennsylvania  limit  this 
number   to    sixty-five   persons,    provided,   however,   that    a 
larger  number,  not  exceeding  one  hundred,  may  be  permitted 
to  work  on  a  single  current  at  the  discretion  of  the  mine 
inspector    and    with    his    permission.     The    Illinois    State 
Mining  Laws  permit  one  hundred  men  to  work  on  a  single 
current,  giving  the  inspector,  however,  authority  to  reduce 
this    number   in    any    given   case   at   his    discretion.      The 
Indiana  Mining  Law  makes  it  unlawful  for  more  than  fifty 
persons  to  work  on  a'single  air-current  and  further  gives  the 
inspector  authority  'to  reduce  this  number  in  any  particular 
case  at  his  discretion.     For  this  reason,  the  splitting  of  the 
air-current  in  a  mine  is  important  aside  from  the  question  of 
producing   a  larger  volume   of   air  by  the   same   power  or 
decreasing  the  power  required  to  circulate  a  given  quantity 
of  air.  

AIR    SPLITS 

7.  Designation    of    Split. — When    an    air-current    is 
divided  into  two  or  more  branches,  it  is  said  to  be  split 
once,   twice,   or  three  times,  according   to    the  number  of 
times  it  is  divided.     When  an  air-current  is  split  once,  it 
travels  in  two  separate  splits  or  currents,  each  branch  being 
termed  a  split.     In  this  sense,  the  number  of  splits  in  a  mine 
is  understood  as  meaning  the  number  of  currents  into  which 
the  main  current  is  divided. 


§14  MINE  VENTILATION  9 

A  split  or  division  of  the  main  current  is  called  a  main 
split,  primary  split,  or  split  of  the  first  degree;  a  split  or 
division  of  a  primary  split  is  called  a  secondary  split,  or  split 
of  the  second  degree;  a  split  or  division  of  a  secondary  split  is 
called  a  tertiary  split,  or  split  of  the  third  degree.  Equal  splits 
are  equal  divisions  of  the  air-current,  provided  that  the 
division  of  the  air  is  natural  and  not  accomplished  by  the 
use  of  a  regulator.  The  length  of  a  split  is  the  length  of 
the  air-current  from  the  point  of  split  to  the  point  where 
the  current  is  again  divided,  or  to  the  point  where  it  joins 
another  current.  A  free,  or  open,  split  is  one  in  which  the 
entire  length  of  the  airway  is  unobstructed  by  any  form  of 
regulator  or  device  for  gauging  the  quantity  of  air  passing 
in  that  split.  The  resistance  of  a  free  or  open  split  is  always 
the  natural  frictional  resistance  of  the  airway. 

8.  Natural  Division  of  the  Air-Current. — Whenever 
there  are  two  or  more  airways  by  which  the  air  may  travel  in 
its  passage  through  the  mine,  the  current  will  divide  naturally 
between  these  airways,  the  quantity  of  air  passing  in  each 
airway  being  proportional  to  the  resistance  of  each  airway; 
the  division  is  then  called  a  natural  division  of  the  air. 

9.  Proportionate  Division  of  the  Air-Current. — It 

generally  happens  in  mining  practice  that  the  natural  divi- 
sion of  the  air-current  does  not  meet  the  requirements  in  the 
mine.  For  example,  the  longer  the  airway  and  the  greater 
the  number  of  men  employed,  the  greater  is  the  amount  of 
air  required,  and,  vice  versa,  the  shorter  the  airway  and  the 
smaller  the  number  of  men  working  on  that  airway,  the 
smaller  is  the  amount  of  air  required.  The  natural  division 
of  the  air,  however,  is  the  reverse  of  this,  the  larger  volume 
of  air  being  circulated  in  the  shorter  airway  and  the  smaller 
volume  in  the  longer  airway.  Therefore,  to  give  the 
required  quantity  of  air  in  the  several  districts  of  the  mine, 
it  is  generally  necessary  to  place  regulators  in  the  airways 
that  naturally  take  more  than  the  desired  quantity  of  air. 
If  the  airways  have  the  same  sectional  area,  this  will  gener- 
ally mean  the  placing  of  regulators  in  all  the  airways  except 


10  MINE  VENTILATION  §14 

the  longest  one,  but  this  is  not  always  the  case,  since  there 
may  be  natural  obstructions  in  one  of  the  shorter  airways 
that  have  the  same  effect  as  increasing  its  length.  In  such 
case,  the  regulator  may  be  required  in  the  longer  airway.  The 
position  of  the  regulator  under  these  varying  conditions  can 
only  be  determined  in  practice  by  the  special  requirements 
in  any  given  case. 

CALCULATIONS   IN   SPLITTING 


NATURAL    SPLITTING 

10.  In  all  calculations  on  the  splitting  of  air-currents,  it 
is  assumed  that  the  pressure  at  the  mouth  of  the  two  or 
more  splits  starting  from  the  same  point  in  the  mine  is  the 
pressure  producing  the  circulation  in  each  split,  and,  there- 
fore, the  pressure  for  all  the  splits  starting  at  one  point  in  a 
mine  is  the  same.  It  will  be  assumed  that  this  is  the  case  in 
the  following  examples  and  also  that  other  conditions  are  the 
same  in  all  the  splits: 

The  quantity  of  air  passing  in  any  airway  may  be  obtained 
from  the  formula, 


As  p  is  assumed  to  be  the  same  for  all  the  splits  and  since  k 
is  also  the  same,  the  quantity  of  air  for  any  split  is  always 

proportional  to  the  expression  a  *  /-,  or  a  -\  /—  for  that  split. 

The  expression  a  .»  /—  is  a  constant  for  any  given  airway 

and  may  therefore  be  conveniently  used  in  comparing  the 
amounts  of  air  circulating  through  two  different  airways. 
This  expression  is  sometimes  called  the  relative  potential 
of  an  airway,  and  for  convenience  it  may  be  represented 
by  X,  and  Xt,  X,,  etc.  will  then  represent  the  relative  poten- 
tials for  the  different  splits  or  airways  compared,  that  is, 


§14  MINE  VENTILATION  11 

Then  if  gt  and  g,  represent  the  quantities  of  air  passing 
through  two  splits, 

I 

_  Xi  /n\ 


Since  the  quantity  of  air  passing  in  any  airway  in  the 
natural  division  of  air  is  proportional  to  the  relative  poten- 
tial for  that  airway,  it  follows  that  the  ratio  of  the  quantity 
of  air  in  any  airway  to  the  total  quantity  of  air  in  circulation 
is  equal  to  the  ratio  of  the  relative  potential  for  that  airway 
to  the  sum  of  the  relative  potentials  of  the  several  airways  or 
splits,  as  expressed  by  the  formula, 


g1  +  q,  +  etc.       Xi+X,+  etc. 


(3) 


It  is  customary  to  denote  the  sum  of  a  series  of  quantities 
or  factors  of  the  same  kind  by  writing  the  plain  symbol  with- 
out any  subscript  with  the  sign  2'  before  it.  Thus,  formula  3 

may  be  written,  -£-  =  ^,-^;   or   calling   the  total  quantity 
2  q        2  X 

Zg  =  Q, 

£1  =  _f*±_  (4) 

Q      SX 

The  relation  expressed  by  this  formula  is  true  in  regard  to 
any  number  of  free  or  open  splits  starting  from  the  same 
point. 

A  few  examples  will  show  the  manner  of  calculating  the 
natural  division  of  a  quantity  of  air  Q  between  two  or  more 
airways  whose  resisting  powers  are  represented  by  the 
potentials  Xlt  X,,  etc. 

EXAMPLE:  1.  —  If  a  current  of  10,000  cubic  feet  of  air  is  passing  in 
the  main  airway  of  a  mine,  how  will  this  quantity  divide  between  two 
splits  or  airways,  one  of  which  is  4  ft.  X  12  ft.  and  6,000  feet  long,  and 
the  other  is  6  ft.  X  8  ft.  and  10,000  feet  long? 

SOLUTION.  —  The  perimeter,    area,  and  length  of   the  first  airway 
are0l  =  2(4  +  12)  =32  ft.,  and  a,  =  4  X  12  =  48  sq.  ft.,  A  =  6,000ft.; 
145—16 


12  MINE  VENTILATION  §14 

for  the  second  airway  o,  =  2(6  +  8)  =  28  ft.,  and  a,  =  6X8  =  48  sq.ft., 
/,  =  10,000  ft.  Calculating  the  relative  potential  for  each  of  these  air- 
ways by  substituting  the  given  values  for  each  respective  airway  in 
the  preceding  formulas, 


Xt  ~  "'  \l,o,  ~  w  \  10,000  X  28 
Before  performing  the  operations  indicated  in  these  expressions,  it 
is  better  to  cancel  all  factors  common  to  both.     This  can  be  done 
because  they  are  to  be  used  as  a  ratio.     Then  canceling  the  factors 
common  to  both  expressions, 

i — l — 

.204 


IX  =  X,  +  X3=  .373 
The  quantity  of  air  passing  in  each  of  these  airways,  respectively. 

is  found  as  follows  from  formula  4,        L^.  =  -&&>  and 

10,000         .0/0 

204 
ql  =  10,000  X  '-zzz  =  5,469,  say  5,500  cu.  ft.  per  min.     Ans. 

.O/O 

a,  .169 

1Q  QQQ  =  -3^3. 

q,  =  10,000  X  4S  =  4.531,  about  4,500  cu.  ft.  per  min.     Ans. 

.O/O 

EXAMPLE  2.— How  will  100,000  cubic  feet  of  air  divide  between  the 
following  three  airways  or  splits?  Split  A,  6  ft.  X  6  ft.  and  2,000  feet 
long;  split  B,  6  ft.  X  5  ft.  and  4,000  feet  long;  split  C,  6  ft.  X  4  ft.  and 
6,000  feet  long. 

SOLUTION. — The  perimeter,  area,  and  length  of  each  of  these  air- 
ways are  as  follows: 

A,    ol  =  2(6  +  6)  =  24  ft.     at  =  6  X  6  =  36  sq.  ft.;  /,  =  2,000  ft. 

30  sq.  ft.;  /,  =  4,000  ft. 
a,  =  6  X  4  =  24  sq.  ft.;  /„  =  6,000  ft. 


Substituting  these  values  in  formula  1, 


§14 


MINE  VENTILATION 


13 


Canceling  the  factors  common  to  all  of  these  expressions,  the  rela- 
tive values  are 

A,  jr.-O-'"^ 


C, 

IX  =  X1  +  X,  +  X3  =  8.085 
Ffnally,  for  the  quantity  of  air  passing  in  each  airway, 

4  242 
A,    g,  =  100,000  X  ^~=  =  52,468,  say  52,500  cu.  ft.  per  min. 


B,    g,  =  100,000  X  ^~  =  29,474,  say  29,500  cu.  ft.  per  min. 

O.UoO 


C,     g3  =  100,000  X         r  =  18,058,  say  18,000  cu.  ft.  per  min. 
Total,     100,000         100,000 


Ans. 


Ans. 


Ans. 


EXAMPLE  3.—  The  velocity  of  the  air-current  in  the  downcast  shaft 
of  a  certain  mine  is  700  feet  per  minute.  The  size  of  the  shaft  is 
15  ft.  X  10  ft.  There  are  at  the  foot  of  this  shaft  four  splits  of 
air  of  the  following  sizes:  Split  A,  5  ft.  X  8  ft.  and  2,000  feet  long; 
split  B,  6  ft.  X  9  ft.  and  1,500  feet  long;  split  C,  7  ft.  X  9  ft.  and 
3,000  feet  long;  split  D,  8  ft.  X  10  ft.  and  1,800  ft.  long.  How 
will  the  air  passing  down  the  shaft  divide  naturally  between  these 
four  splits? 

SOLUTION.  —  The  total  quantity  of  air  passing  into  this  mine  is 
Q  =  av  =  (15  X  10)700  =  105,000  cu.  ft.  per  min.  The  perimeter 
area  and  length  of  each  of  these  airways  is  as  follows: 

A,  o,  =  2(5  +    8)  =  26  ft.;  a,  =  5  X    8  =  40  sq.  ft.;  /,  =  2,000  ft. 

B,  o,  =  2(6  +    9)  =  30  ft.;  a,  =  6  X    9  =  54  sq.  ft.;  /,  =  1,500  ft. 

C,  03  =  2(7+    9)  =  32  ft.;  a3  =  7  X    9  =  63  sq.  ft.;  /,  =  3,000  ft. 
Z7,  o<  =  2(8  X  10)  =  36  ft.;  at  =  8  X  10  =  80  sq.  ft.;  /.  =  1,800  ft. 

A, 


A', 


B, 
C, 


X, 


14  MINE  VENTILATION  §14 

Canceling  the  factors  common  to  all  of  these  expressions,  we  have 
for  the  relative  values, 


*  -  4°       -  4°    =  ^^  =  i5-697 

26'454 


X,  +  X,  +  X3  +  Xt  =  104.712 
Finally,  for  the  quantity  of  air  passing  in  each  airway, 


A,     ql  =  106,000  X  o  =  15,740,  say  15,700  cu.  ft.  per  min. 

104.71^ 

Ans. 


Bt      g,  =  105,000  X  rfr    =  26,527,  say  26,500  cu.  ft.  per  min. 

1U4.  /1Z 

Ans. 

99  809 

C,  g,  =  105,000  X  ifcjfi  =  22>865'  sav  22'900  cu>  ft>  Per  min' 

Ans. 

on  yen 

D,  qt  =  105,000  X  :^r^>  =  39,868,  say  39,900  cu.  ft.  per  min. 

1U4./1Z          --  -  . 

Total,     105,000         105,000 

11.     Pressure  and  Power  Required:   Equal  Splits. 

In  natural  splitting,  when  the  splits  are  equal,  the  total 
quantity  of  air  in  circulation  is  equally  divided  among  all 
the  splits.  The  pressure  at  the  point  of  split  is  the  same 
for  all  the  splits  starting  at  that  point,  whether  the  splits  are 
equal  or  unequal.  When  the  splits  are  equal,  an  equal 
power  is  consumed  in  each  split;  hence,  in  equal  natural 
splitting,  since  the  air  is  equally  divided  among  the  several 
splits,  the  pressure  and  the  power  producing  the  circulation 
in  one  of  these  splits  only  is  first  calculated.  The  pressure 
thus  obtained  for  one  split  is  the  same  for  all  the  splits,  and 
is  the  pressure  producing  the  total  circulation  in  the  splits. 
It  must  be  remembered  that  the  same  pressure  on  the  air  at 
the  point  of  split  circulates  the  air  in  all  the  splits  starting 
from  that  point.  The  power  producing  the  circulation  in  one 
split,  however,  must  be  multiplied  by  the  number  of  splits  in 
order  to  obtain  the  power  producing  the  total  circulation; 
or  the  total  power  producing  the  circulation  may  be  found 


§14  MINE  VENTILATION  15 

by  multiplying  the  pressure  at  the  point  of  split  by  the  total 
quantity  of  air  in  circulation  in  all  the  splits.  An  example 
will  make  this  point  clear. 

EXAMPLE. — Find  the  unit  of  ventilating  pressure  and  the  power 
required  to  circulate  90,000  cubic  feet  of  air  per  minute  in  three  equal 
splits,  each  being  6  ft.  X  10  ft.  and  2,000  feet  long. 

SOLUTION. — The  splits  being  equal,  the  quantity  of  air  passing  in 
each  will  be  ^i^  =  30,000  cu.  ft.  per  min.  The  perimeter  and  area 
of  each  of  these  splits  are  as  follows:  o  =  2(6  +  10)  =  32  ft.; 
a  =  6  X  10  =  60  sq.  ft.  Substituting  the  given  values  in  the  formula 
for  pressure, 
f  _  tlof,  _  .OCXXXXX.2X  2,000X32X80,000-  .  SJa+  ,b  per  sq  ^ 

which  is  the  unit  of  ventilating  pressure  at  the  point  of  split,  or  the 
pressure  per  square  foot  producing  the  circulation  in  all  the  splits. 

Ans. 

The  power  required  to  circulate  30,000  cu.  ft.  of  air  per  min.  in  a 
single  split  6  ft.  X  10  ft.,  2,000  ft.  long,  is  found  by  substituting  the 
given  values  in  the  formula  for  power,  thus, 

u_*!*t_  .00000002  X2.0MX  32X30,000-  _  „„,_„„,  ft  .,„ 

The  total  power  consumed  in  the  three  splits  is  then  3  X  160,000 
=  480,000  ft.-lb.,  or  480,000  4-  33,000  =  14.545+  H.  P.  Ans. 

The  same  result  would  have  been  found  by  multiplying  the  unit  of 
ventilating  pressure  first  found  by  the  total  quantity  of  air  in  circula- 
tion as  expressed  by  the  formula  u  =  qp  =  90,000  X  5.33  =  479,700  or 
about  480,000  ft.-lb.  Ans. 

12.     Pressure  and  Power  Required:  Unequal  Splits. 

When  two  or  more  splits  starting  from  the  same  point  in  a 
mine  are  unequal  in  length  or  sectional  dimensions,  the  air 
will  be  divided  unequally  between  the  several  splits.  While 
the  pressure  per  square  foot  at  the  point  of  split  is  the  same 
for  each  split,  a  different  power  will  be  consumed  in  each 
split.  The  first  step  in  this  case  is  to  calculate  the  natural 
division  of  the  air,  or,  in  other  words,  to  find  the  quantity  of 
air  passing  in  each  split.  The  pressure  per  square  foot  pro- 
ducing the  circulation  in  each  split,  which  is  the  pressure 
producing  the  total  circulation  in  all  the  splits  starting  from 
that  point,  may  then  be  found  by  calculating  the  pressure 
necessary  to  circulate,  in  any  one  split,  the  quantity  of  air 
thus  calculated.  Having  found  the  pressure  per  quare  foot 


16  MINE  VENTILATION  §14 

for  any  one  split  or  the  pressure  producing  the  total  circu- 
lation in  all  the  splits,  the  total  power  producing  the  circula- 
tion is  then  found  by  multiplying  this  pressure  by  the  total 
quantity  of  air  in  circulation.  An  example  will  make  this 
calculation  clear. 

EXAMPLE.— (a)  Find  the  unit  of  ventilating  pressure  that  will  cir- 
culate 90,000  cubic  feet  of  air  per  minute  in  three  splits  as  follows: 
Split  A,  6  ft.  X  10  ft.  and  3,000  feet  long;  split  B,  5  ft.  X  9  ft.  and 
2,500  feet  long;  split  C,  5  ft.  X  6  ft.  and  1,500  feet  long,  (b)  What 
is  the  power  on  the  air  at  the  point  of  split? 

SOLUTION. —  The  perimeter,  area,  and  length  in  each  split  are  as 
follows: 

A,    o,  =  2(6  +  10)  =  32  ft.;  a,  =  6  X  10  =  60  sq.  ft.;  /t  =  3,000  ft. 

£,    o,  =  2(5  +    9)  =  28  ft.;  a,  =  5  X    9  =  45  sq.  ft.;  /,  =  2,500  ft. 

C,    o3  =  2(5  +    6)  =  22  ft.;  aa  =  5  X    6  =  30  sq.  ft.;  /,  =  1,500  ft. 

Then,  to  calculate  the  natural  division  of  the  air  between  these  three 

splits,  substitute  the  values  for  these  airways  in  formula  1  of  Art.  1O, 

A, 

B'  "•—        -w -2,600X28 

—  i 

fl3 

*    'l300X22 

Then,  canceling  the  factors  common  to  all  these  expressions, 
T 


A, 


Ct  Xa  ~  ~  \3  X  11 

I  X  =  Xl  +  X,  +  X3  =  1.929 
Then,  for  the  quantity  of  air  passing  per  minute  in  each  split, 

A,  q,  =  90,000  X  j^  =  38,070 

B,  q*  =  90,000  X  ~jjy  =  28,970 

C,  q*  =  90,000  X  f~  =  22,960 

Total,     90,000 

(a)  The  unit  of  ventilating  pressure  may  now  be  calculated  in  the 
usual  manner  from  any  of  these  splits,  the  same  value  being  found  in 
each  case  as  follows: 


§14  MINE  VENTILATION  17 

k  lo  q*       .00000002  X  3,000  X  32  X  38,070* 
A,  p=  —j3-  — w- 

=  12.88  Ib.  per  sq.  ft.     Ans. 
kloq*        .00000002  X  2,500  X  28  X  28,970' 
B*  P  =  ~~a^  ~&r~ 

=  12.89  Ib.  per  sq.  ft.     Ans. 

_  kloq*        .00000002  X  1,500  X  22  X  22,960' 

C>  p  =  —*  30' 

=  12.88  Ib.  per  sq.  ft.     Ans. 

It  is  only  necessary  to  calculate  the  pressure  for  one  split,  since  this 
pressure  is  the  same  for  all  the  splits  starting  from  the  same  point  in 
the  mine.  It  is  the  pressure  at  the  mouth  of  these  splits.  In  speaking 
of  ventilating  pressure,  the  difference  of  pressure  between  the  intake 
and  return  airways  at  this  point  is  meant;  it  is  not  the  total  pressure 
on  the  air. 

(b)  The  power  required  to  circulate  90,000  cu.  ft.  in  splits  A,  B, 
and  Cin  this  case  is  then  found  by  substituting  the  values  for  the  quan- 
tity and  unit  of  ventilating  pressure  in  the  formula  for  power;  thus, 

u  =  qp  =  90,000  X  12.88  =  1,159,200  ft.-lb. 
or  for  the  horsepower 

h_     qP     _  90.000  X  12.88  _ 

*       33^000  33,000  H'  R     Ans' 

The  pressure  and  the  power  required  to  circulate  a  given 
quantity  of  air  in  any  number  of  unequal  splits  can  be  found 
directly  and  more  quickly  by  the  use  of  the  following 
formula: 

:        .      '-(ft)'         <« 

in  which       p  =  pressure  in  pounds  per  square  foot; 
k  =  .00000002; 
Q  =  total  quantity  of  air  in  circulation; 


For  the  sake  of  comparison,  the  example  in  Art.  12,  when 
worked  by  this  formula,  gives  the  following  solution: 
SOLUTION.— As  before, 


A,  ol  =  2(6  +  10)  =  32ft.;  a»  =  6  X  10  =  60  sq.  ft. 

B,  o,  =  2(5  +    9)  =  28  ft.;  a,  =  5  X    9  =  45  sq.  ft. 

C,  oa  =  2(5  +    6)  =  22  ft.;  a,  =  5  X    6  =  30  sq.  ft. 


/,  =  3,000  ft. 
/,  =  2,500  ft. 
/3  =  1,500ft. 


18  MINE  VENTILATION  §14 

Then,  substituting  these  values  in  formula  1  of  Art.  1O,  for  airways 

•.»•  «yv    .      I  60 

..'  / , 


c, 

••  3.5454 

Then,  substituting  the  given  values  in  the  formula  for  the  unit  of 
ventilating  pressure  circulating  90,000  cu.  ft.  of  air  in  these  three  splits, 

p  =  k  UQ  '  =  .00000002  (|°5-^)  "  =  12.88  Ib.  per  sq.  ft. 

The  power  required  to  circulate  90,000  cu.  ft.  of  air  per  min.  in 
splits  A,  B,  and  C  is  then  found  by  multiplying  the  pressure  by  the 
quantity  in  the  same  manner  as  before;  thus, 

qp     _  90,000  X  12.88  _ 
~  33,000  33JOOO  '          S' 

13.     Total    Mine    Pressure    and    Power    Required. 

The  main  air-current  in  a  mine,  after  passing  down  the 
shaft,  is  often  conducted  for  a  considerable  distance  through 
a  single  airway  before  reaching  the  place  where  the  air  is  to 
be  divided.  This  requires  that  the  entire  circulation  be 
carried  for  a  certain  distance  through  a  single  air  conduit, 
which  includes  the  upcast  and  downcast  shafts  and  the  main 
intake  and  return  airways  outside  of  the  point  of  split.  In 
this  case,  the  total  pressure  producing  the  circulation  in 
the  mine  is  equal  to  the  sum  of  the  pressures  absorbed 
in  passing  the  air  through  the  two  shafts  and  the  main 
airways  and  the  splits,  respectively.  If  desired,  each  tof 
these  pressures  may  be  calculated  separately  by  the  for- 
mulas and  methods  previously  described  for  finding  the 
unit  of  ventilating  pressure.  The  operation,  however,  is 

much  shortened  by  calculating  the  expression  a+  I—  for  each 

section  of  the  air  passage,  namely,  the  shafts,  main  airways, 
and  the  splits,  and  substituting  these  values  in  the  following 
formula 


§14  MINE  VENTILATION  19 

in  which    p  =  pressure,  in  pounds  per  square  foot; 
k  =  .00000002; 
Q  =  quantity  of  air  circulating; 

XltX,,X,  =  constant  a-\\j-  for  several  parts  of  the   air- 

current  that  are  not  split,  such  as  in.  the 
upcast,  main  airway,  etc. 

Xf  =  sum   of  constants  e\lj-    calculated  for   the 

several  splits  of  air. 

This  formula  applies  alike  when  the  splits  are  equal  or 
unequal  and  may  be  extended  indefinitely  so  as  to  include  any 
sections  of  the  airway  having  different  cross-sections  by  find- 
ing the  values  of  Xlt  X*,  etc.  for  each  section  of  the  airway, 
but  always  using  the  sum  of  these  constants  for  the  several 
splits  in  determining  the  value  I  XP.  If  there  are  no  splits 
in  the  mine,  the  last  term  containing  I  Xp  will  disappear. 

The  following  example  will  show  the  manner  of  using 
this  formula: 

EXAMPLE.  —  In  a  shaft  mine,  the  downcast  shaft  is  6  ft.  X  14  ft.; 
the  upcast  shaft,  8  ft.  X  12  ft.;  both  shafts  being  1,000  feet  deep.  At 
a  point  100  feet  from  the  foot  of  the  downcast  shaft  the  air-current  is 
divided  into  two  splits;  these  splits  unite  100  feet  before  reaching  the 
foot  of  the  upcast.  The  size  of  the  main  intake  and  main  return  airways 
from  the  foot  of  each  shaft  to  the  splits  is  6  ft.  X  12  ft.  and  100  feet 
long  for  each  airway.  The  air  split  ventilating  the  east  portion  of  the 
mine  called  the  east  split  is  5  ft.  X  9  ft.  and  2,500  feet  long,  while  the 
west  split  is  5  ft.  X  8  ft.  and  1,500  feet  long.  What  pressure  and 
power  will  be  required  to  circulate  75,000  cubic  feet  of  air  per  minute 
in  this  mine  when  no  regulators  are  used  to  divide  the  air? 

SOLUTION.  —  The  perimeter,  area,  and  length  of  the  downcast  and 
upcast  shafts,  the  main  intake  and  main  return  airways,  and  the  east 
and  west  splits,  respectively,  are  as  follows: 

Downcast  shaft,  o,  =  2(6  +  14)  =  40  ft;  a,  =  6  X  14  =  84  >q.  ft.; 
A  =  1,000  ft. 

Upcast  shaft,  o,  =  2(8  +  12)  =  40  ft.;  a,  =  8  X  12  =  96  sq.  ft.; 
/,  =  1,000  ft. 

' 


/,  =  200  ft. 


20 


MINE  VENTILATION 


§14 


East  split,  ot  =  2(5  +9)  =28  ft.;  a«  =  5  X  9  =  45  sq.  ft.; 
/.  =  2,500  ft. 

West  split,  0,  =  2(5  +  8)  =  26  ft.;  a,  =  5  X  8  =  40  sq.  ft.; 
/.  =  1,500  ft. 

Then  for  the  several  airways, 

Downcast  shaft,     " 

Upcast  shaft, 

Main  airways,       X,  =  72 


East  split, 
West  split, 


™  =  1.2810 


'1,500X26 
Xt  +  X*  =  IXP  =  2.4219 

Substituting  the  given  values  in  the  formula  for  the  unit  of  venti- 
lating pressure  producing  the  circulation, 

p  =  .00000002  X  75,000'  (ggjgji  +  5-^  +  7^  +  2l2l9^)  =  34'03> 

or  about  34  Ib.  per  sq.  ft. 

The  power  producing  this  circulation  is  then  found  by  multiplying 
the  unit  of  ventilating  pressure  by  the  total  quantity  of  air  passing 
into  the  mine  and  dividing  by  33,000;  thus, 
_  75.000  X  34  _ 

~~33^000       ~77'J7-    Ans" 


PROPORTIONATE    SPLITTING 

14.  Any  division  of  the  air-current  other  than  the  natural 
division  that  takes  place  when  all  the  airways  are  open  to  the 
passage  of  the  air  is  called  a  proportionate  division.  The  air 
is  then  divided  between  the  several  parts  of  the  mine  accord- 
ing to  the  needs  or  requirements  in  each  district,  by  means 
of  regulators  such  as  were  described  in  Mine  Ventilation, 
Part  1.  A  regulator  placed  in  an  airway  has  the  same  effect 
as  lengthening  the  airway  and  thus  increasing  its  resistance. 
The  natural  frictional  resistance  of  the  airway  is  increased 
by  the  resistance  due  to  the  regulator. 

In  proportionate  splitting,  as  in  natural  splitting,  the  pres- 
sure per  square  foot  at  the  point  of  split  is  equal  for  all 


§14  MINE  VENTILATION  21 

splits  starting  from  the  same  point.  It  is  therefore  evident 
that,  for  any  desired  proportionate  splitting  of  the  air-current 
in  a  mine,  that  split  having  the  greatest  natural  pressure  per 
square  foot,  calculated  for  the  desired  quantity  of  air,  will 
be  the  open  or  free  split,  and  all  the  other  splits  must  be 
supplied  with  regulators  so  arranged  as  to  increase  the  pres- 
sure in  each,  so  as  to  make  the  pressure  per  square  foot  at 
the  point  of  split  equal  for  all  the  splits  starting  from  this 
point.  An  example  will  show  the  method  of  making  the 
calculation  necessary  to  determine  in  which  splits  regulators 
should  be  placed  to  accomplish  any  required  division  of  the 
air-current. 

EXAMPLE. — Where  must  regulators  be  placed  and  what  must  be  the 
size  of  the  opening  in  each  in  order  to  produce  the  following  circula- 
tion of  air? 

Split^,  6  ft.  X  10  ft.,  3,000  feet  long,  50,000  cu.  ft.  per  min.; 
Split  jS,  5  ft.  X  9  ft.,  2,500  feet  long,  30,000  cu.  ft.  per  min.; 
Split  C,  5  ft.  X  6  ft.,  1,500  feet  long,  10,000  cu.  ft.  per  min. 

What  will  be  the  pressure  per  square  foot  at  the  point  where  the  air 
is  divided,  and  what  horsepower  will  be  required  for  the  circulation  of 
the  air  in  the  splits? 

SOLUTION. — This  is  the  same  mine  described  in  the  example  in 
Art.  12  where  the  natural  division  of  the  air  was  found  to  be  approxi- 
mately as  follows:  Split  A,  38,000  cu.  ft.;  split  B,  29,000  cu.  ft.; 
split  C,  23,000  cu.  ft. 

The  natural  pressure  for  each  split  may  be  found  by  substituting  in 

the  general  formula  for  pressure,^  =  —^  as  follows: 

At    f:  _  .00000002X3.^X32X60,000-  _  ^  [b  pcr  sq   ft 

B    ff  _  .00000002X2,^X28X30,000-  _  ^  ,b  per  ^   ft 
c               00000002  X  1,500  X  22  X  IQ.OOOJ  =    i-44  ,„  „. 

oU 

The  natural  pressure  may  also  be  calculated  by  first  calculating  the 
relative  potential  for  each  split  and  substituting  in  the  formula 

p  =  k~  as  follows: 
JL 

The  relative  potentials  for  these  splits  were  found  in  Art.  12  to  be 
Xl  =  1.5;  X,  =  1.1409;  X,  =  .9045. 


22  MINE  VENTILATION  §  14 

Then,  A,  p,  =  .00000002  l^~Y=  22.22  Ib.  per  sq.  ft. 
B,pt=  .00000002  (i°i4^)2=  13-82  Ib.  per  sq.  ft. 

c,  pa  =  .00000002  (-S^)*=  2-44  lb-  Per  sq-  ft- 

Split  A  having  the  greatest  natural  pressure  will  therefore  be  the 
open  or  free  split,  and  this  pressure  of  22.22  pounds  per  square  foot 
will  be  the  ventilating  pressure  at  the  point  of  split  where  the  air  is 
divided.  Regulators  must  be  placed  in  splits  B  and  C.  The  openings 
in  these  regulators  are  found  by  first  calculating  the  pressure  due  to 
each  regulator  in  inches  of  water  gauge  by  subtracting  the  natural 
pressure  for  each  split  from  the  ventilating  pressure  at  the  point  of 
split  and  dividing  by  5.2;  thus, 


,  .  g  . 

C,  i.  -*•*'-*•"-  3.8  in. 

O.^ 

The  openings  in  these  two  regulators  are  then  found  by  substituting 
the  values  thus  obtained  in  the  formula  for  finding  the  area  of  the 
opening  in  a  regulator  (Art.  42,  Mine  Ventilation,  Part  1);  thus, 
B,      a,  =  .00038  -&=  =  .00038X30.000  =  of  g 


C,       a3  =  .00038  -^  =   .00038X10.000  -  1.95,  or  2  sq.  ft. 

VT,  V^8 

The  regulator  in  split  B  should  therefore  have  an  opening  of  9  square 
feet,  and  that  in  split  C  an  opening  of  2  square  feet. 

The  pressure  per  square  foot  at  the  point  of  split  where  the  air  is 
divided  is  equal  to  the  natural  pressure  producing  the  circulation  in 
the  open  split,  split  A,  and  is  22.22  pounds  per  square  foot. 

The  total  horsepower  producing  the  circulation  in  splits  A,  B,  and  C 
is  found  by  multiplying  the  total  quantity  of  air  in  circulation  by  the 
pressure  at  the  point  of  split  and  dividing  by  33,000;  thus, 


EXAMPLES    FOR    PRACTICE 

1.  In  a  certain  mine,  the  total  quantity  of  air  passing  down  the 
downcast  shaft  is  45,000  cubic  feet  per  minute;  at  the  foot  of  the  down- 
cast, it  is  divided  into  four  splits  as  follows:  Split  A,  6  ft.  X  6  ft.  and 
1,500  feet  long;  split  B,  6  ft.  X  7  ft.  and  1,800  feet  long;  split  C,  6  ft. 
X  5  ft.  and  1,350  feet  long;  split  D,  5  ft.  X  5  ft.  and  1,500  feet  long. 


§14  MINE  VENTILATION  23 

Calculate  the  amount  of  air  passing  in  each  split  when  no  regulators 
are  used.  [A,  12,582  cu.  ft.  per  min. 

.        \B,  13,905  cu.  ft.  per  min. 

Ans>  1  C,  10,537+  cu.  ft.  per  min. 
1/7,  7,976+  cu.  ft.  per  min. 

2.  A  current  of  60,000  cubic  feet  of  air  per  minute  is  circulated  in 
a  certain  mine  in  five  splits  as  follows:     Split  A,  8,000  cubic  feet; 
split  JB,   10,000  cubic  feet;  split  C,  12,000  cubic  feet;  split  D,  14,000 
cubic  feet;  split  E,  16,000  cubic  feet.     Calculate  the  sectional  area  for 
each  split  in  order  that  the  air  may  travel  at  a  uniform  velocity  of 
5  feet  per  second  in  all  the  splits.  (A,  26f  sq.  ft. 

B,  33i  sq.  ft. 

Ans.^C,  40    sq.  ft. 

\D,  46|  sq.  ft. 

\E,  53i  sq.  ft. 

3.  How  will  an  air-current  of    10,000  feet   per   minute   divide  if 
split  A  is  4  ft.  X  12  ft.  and  6,000  feet  long  and  split  B  is  6  ft.  X  8  ft. 
and  10,000  feet  long?  A       fA,  5,470  cu.  ft.  per  min. 

ls-\^,  4,530  cu.  ft.  per  min. 

4.  How  will   an    air-current   of   50,000  feet  per  minute  divide  if 
split  A  is  5  ft.  X  8  ft.  and  3,000  yards  long  and  split  B  is  6  ft.  X  9  ft. 
and  5,000  yards  long?  An    fA,  23,462-  cu.  ft.  per  min. 

\£t  26,538+ cu.  ft.  per  min. 

5.  (a)  Calculate  the  natural  division  of    150,000  cubic  feet  of  air 
between  the  following  splits:     Split  A,  8  ft.  X  9  ft.  and  4,000  feet  long; 
split  B,  6  ft.  X  9  ft.   and  3,500  feet  long;   split   C,  8  ft.  X  12  ft.   and 
5,000  feet  long,     (b)  Where  should  regulators  be  placed  in  order  to 
accomplish  the  following  division  of  air  in  these  airways:  Split  A,  60,000 
cubic  feet;   split  B,   50,000   cubic    feet;    split    C,    40,000   cubic   feet? 
(c)  Calculate  the  size  of  the  opening  in  each  regulator. 

A,  49,853  cu.  ft.  per  min. 
(a){B,  36,852  cu.  ft.  per  min. 
C,  63,295  cu.  ft.  per  min. 
Regulators  should  then  be  placed 


Ans. 


in  A  and  C,  B  being  the  open 
or  free  split 

Area  of  opening  in  regulator  in 
A  is  19. 55  sq.  ft.;  area  of  open- 
ing in  regulator  in  C  is  6.78 
sq.  ft. 


24  MINE  VENTILATION  §14 


VENTILATION  OF  A  MINE 


PRACTICAL     CONSIDERATIONS 

15.  The  efficient  ventilation  of  a  mine  is  dependent  on 
four  essential  elements:     (a)  Volume  of  the  current  or  quan- 
tity of  air  in  circulation;   (b)  distribution  of  the  air  in  the 
mine  workings;   (c)  velocity  of  the  air-current;   (d)  manner 
of  conducting  the  air-current.   ' 

The  proper  ventilation  of  a  mine  requires  that  a  quantity 
af  air  should  be  passing  into  the  main  intake  airway  suffi- 
cient to  meet  the  requirements  of  the  mining  law  of  the  state 
in  which  the  mine  is  located.  This  volume  of  air  must  be 
so  divided  between  the  several  districts  of  the  mine  that 
each  district  will  receive  a  sufficient  quantity  of  air  to  dilute, 
sweep  away,  and  render  harmless  the  gases  produced  in 
that  district.  The  abandoned  workings  and  falls  must  be 
thoroughly  ventilated.  The  velocity  of  the  air-current  at  the 
working  face  must  be  such  that  there  will  be  no  accumula- 
tions of  gas  in  the  cavities  of  the  roof  and  other  void  spaces. 
In  a  gaseous  mine  the  velocity  of  the  air-current  at  the  work- 
ing face  should  not  exceed  8  feet  per  second  or  about  500 
feet  per  minute.  For  reasons  of  economy,  at  least,  it  is 
important  that  all  the  air  taken  into  any  given  part  of  a  mine, 
except  what  is  required  for  the  ventilation  of  stables,  pump 
rooms,  etc.,  should  be  made  to  sweep  the  working  face. 
This  can  be  accomplished  only  by  building  substantial  air- 
tight stoppings  in  the  cross-cuts  between  the  airways,  and, 
where  necessary,  by  special  brattices  to  deflect  the  air-current 
so  that  it  will  sweep  any  cavities  or  lodging  places  for  gas 
in  the  roof  or  sides  of  a  passageway. 

16.  Quantity  and  Velocity  of  Air  Required. — It  is 

customary  to  estimate  the  quantity  of  air  required  for  the 


§14  MINE  VENTILATION  25 

ventilation  of  a  mine  on  a  basis  of  100  cubic  feet  or  more 
per  man  per  minute,  and  from  five  to  six  times  this  amount 
per  horse  or  mule  per  minute,  the  amount  depending  on  the 
gaseous  condition  of  the  mine.  This  is  an  arbitrary  stand- 
ard without  reference  to  the  fact  that  a  high  and  often 
dangerous  velocity  of  the  air  may  be  necessary  to  produce 
this  amount  of  air  in  the  contracted  airways  of  thin  seams 
and  that  only  a  low  and  inefficient  velocity  would  be  needed 
to  give  the  same  quantity  in  the  larger  airways  of  thick 
seams.  As  the  velocity  in  the  airways  and  at  the  working 
face  should  be  maintained  within  certain  prescribed  limits 
it  must  be  considered  in  connection  with  the  amount  of  air 
required. 

In  a  mine  generating  marsh  gas,  the  velocity  of  the  air  in 
the  workings  should  not  exceed  8  feet  per  second  or  480  feet 
per  minute,  while  in  any  case  the  velocity  at  the  working 
face  should  not  fall  below  3  or  4  feet  per  second,  or  about 
200  feet  per  minute.  In  the  absence  of  gas,  the  velocity 
on  the  main  airways  often  varies  from  600  to  1,500  feet  per 
minute.  The  velocity  of  the  air-current  is  an  important  con- 
sideration where  gas  is  given  off  in  large  quantities,  since  a 
sluggish  current  having  a  low  velocity  will  not  remove  the 
heavy  gases  from  the  Ipwer  or  dip  workings  or  the  lighter 
gases  from  the  rise  workings.  The  removal  of  large  bodies  of 
gas  from  rise  or  dip  workings  often  requires  that  the  velocity 
of  the  air-current  be  temporarily  increased  beyond  what  is  a 
safe  working  velocity  of  the  air-current.  It  must  be  remem- 
bered that  a  safety  lamp  carried  against  an  air-current  is  sub- 
jected to  a  current  velocity  equal  to  the  velocity  of  the  air  plus 
the  velocity  with  which  the  lamp  is  moving.  For  this  reason 
it  is  well,  if  possible,  in  the  examination  of  main  airways  to 
travel  with  the  air  and  to  carefully  protect  the  lamp  from  the 
air-current  when  it  is  necessary  to  halt  in  the  airway. 

17.     Quantity  of  Air  Required  by  t,aw. — The  Anthra- 
cite Mining  Laws  of  Pennsylvania  (Art.  X,  Sec.  7)  provide 
that  all  air  passages  shall  be  of  sufficient  area  to  allow  the. 
free  passage  of  not  less  than  200  cubic  feet  of  air  per  minute 


26  MINE  VENTILATION  §14 

for  every  person  working  therein,  and  a  velocity  not  to  exceed 
450  feet  per  minute  where  safety  lamps  are  used,  except  in 
the  main  intake  and  return  airways.  Not  more  than  seventy- 
five  persons  are  permitted  by  law  to  work  in  the  same  air 
split,  except  by  special  permission  from  the  mine  inspector. 

The  Bituminous  Mining  Laws  of  Pennsylvania  provide 
that  the  minimum  quantity  of  air  shall  not  be  less  than 
100  cubic  feet  per  minute  for  every  person  employed  in  a 
mine;  but  in  a  mine  where  firedamp  has  been  detected  the 
minimum  shall  be  150  cubic  feet,  and  as  much  more  in  either 
case  as  one  or  more  of  the  mine  inspectors  may  deem 
requisite.  It  limits  the  number  of  men  working  in  an  air 
split  to  sixty-five.  The  law  in  Illinois  provides  for  100  cubic 
feet  per  minute  for  each  person  and  600  cubic  feet  per  minute 
for  each  animal,  measured  at  the  foot  of  the  downcast,  but 
this  amount  may  be  increased  at  the  discretion  of  the  mine 
inspector.  The  number  of  men  in  any  one  split  is  limited  to 
100,  or  less,  at  the  discretion  of  the  mine  inspector. 

The  amounts  of  air  and  the  number  of  men  allowed  in  a 
split  as  given  above  are  simply  examples  of  state  laws,  and 
as  they  are  subject  to  change  from  time  to  time  they  should 
not  be  used  in  answering  examination  questions,  but  the 
latest  law  for  each  state  should  be  consulted. 


VENTILATION    OF    DIFFERENT    TYPES    OF    MINES 

18.  Ventilation  of  a  Drift  Mine. — The  simplest  case 
of  mine  ventilation  is  where  the  seam  lies  flat  or  nearly  so 
and  where  the  mine  is  entered  by  a  practically  horizontal 
passageway,  called  a  drift  when  it  is  driven  in  the  coal  or  a 
tunnel  when  it  is  driven  in  the  rock.  In  the  plan>  Fig.  2, 
the  entrance  to  the  mine  is  shown  at'  the  top  of  the  illustra- 
tion. The  main  drift  and  haulage  road  a  is  usually  made  the 
intake  airway.  An  upcast  shaft  may  be  sunk  at  a  con- 
venient point  where  it  is  easily  reached  by  the  main  return 
airway  of  the  mine  and  where  the  depth  of  the  seam  below 
the  surface  is  as  small  as  possible,  so  as  to  decrease  the  cost 
of  sinking  the  shaft;  or  the  return  airway  b,  Fig.  2,  may  be 


§14 


MINE  VENTILATION 


27 


parallel  to  the  intake  and  the  ventilator  placed  at  the  mouth 
of  this  return.  Any  form  of  mine  ventilator  may  be  used  to 
produce  the  circulation.  The  mine  is  divided  into  sections 
by  cross-entries  c,  d  and  <?,  /  driven  in  pairs  as  shown.  The 
main  air-current  passing  along  the  main  drift  or  air-course  a 
is  divided  at  the  mouth  of  each  pair  of  cross-entries  as  shown 
at  g  and  h,  one  split  of  the  air  continuing  along  the  main 
airway  and  the  other  passing  along  the  side  entry  through  a 
cross-cut  near  the  face  of  the  entry  and  back  along  the 


FIG.  2 

return  c  or  ^,  as  indicated  by  the  arrows.  The  crossed  lines 
at  the  mouth  of  one  entry  of  each  pair  of  cross-entries  at  i 
and  j  indicate  the  position  of  overcasts.  The  one  at  i  carries 
the  return  air  from  the  entry  c  to  the  return  airway  b. 
The  overcast  j  carries  the  main  return  air,  passing  in  b,  over 
the  haulage  road  /.  The  dotted  lines  in  the  center  of  the 
intake  entries  show  the  position  of  the  haulage  track  and 
indicate  the  haulage  roads  of  the  mine,  which  maintain  a 
continuous  grade,  while  any  air  crossings  pass  over  or  under 
them.  Before  the  cross-entries  have  reached  a  stage  of 

145—17 


28  MINE  VENTILATION  §14 

development  requiring  the  building  of  an  air  bridge,  doors 
are  used  to  deflect  the  main  current  into  these  entries. 

19.  Ventilation  of  Slope  or  Shaft  Mines:  Flat 
Seams. — The  ventilation  of  a  flat  seam  opened  by  a  slope 
or  shaft  differs  from  the  ventilation  of  a  drift  mine  just 
described  only  in  the  arrangements  about  the  bottom  of  the 
slope  or  shaft  in  connection  with  the  hoisting  of  the  loaded 
cars  to  the  surface,  the  underground  stables,  etc.,  which  are 
not  generally  needed  at  a  drift  mine.  In  the  case  of  a  shaft 
or  slope  mine,  the  main  hoisting  shaft  or  slope  is  generally 
used  either  as  a  main  intake  or  a  return  for  the  air.  Another 
shaft  or  slope  not  far  from  the  first  is  used  as  a  return  or 
intake,  depending  on  which  way  the  air  passes  through  the 
main  shaft.  Sometimes,  and  especially  if  the  mine  has  been 
extended  for  some  distance  from  the  main  shaft,  an  air-shaft 
or  slope  is  sunk  to  some  point  in  the  inside  workings  for  the 
purpose  of  shortening  the  distance  the  air  must  travel  in 
passing  through  the  mine,  and  furnishing  more  direct  circu- 
lation of  air  through  the  mine.  In  order  to  avoid  the  use 
of  doors  on  the  main  haulage  road  at  the  bottom  of  the 
shaft  or  slope,  it  is  necessary  to  use  an  exhaust  fan  when 
the  hauling  is  done  on  the  intake  airway,  and  a  blower  fan 
when  hauling  is  done  on  the  return  airway  of  the  mine. 

The  important  feature  with  reference  to  the  ventilation  of 
a  shaft  or  slope  bottom  is  to  so  arrange  the  airways  as  to 
furnish  the  most  direct  passage  for  the  air-currents  between 
the  bottom  of  the  shaft  and  the  mine  workings.  Provision 
must  be  made  in  this  arrangement  for  the  future  develop- 
ment of  the  mine  and  for  the  ventilation  of  the  stables, 
pump  rooms,  hospital,  tool  and  other  shanties  or  wash 
rooms,  and  also  so  that  the  main  air-current  may  be  split  as 
near  as  possible  to  the  foot  of  the  downcast  shaft.  The 
stables,  if  possible,  should  be  located  between  the  upcast 
and  downcast  shafts  so  as  to  secure  better  ventilation  of  the 
stables  and  to  make  them  of  easy  access  in  case  of  accident 
and  also  to  keep  the  stable  air  from  circulating  through  the 
mine.  Two  arrangements  of  the  circulation  and  airways, 


§14 


MINE  VENTILATION 


29 


stables,  etc.  at  the  bottom  of  a  shaft  are  shown  in  Figs.  3 
and  4.  In  each  of  these,  the  mine  stables  are  ventilated  by 
a  separate  split  of  air  taken  off  the  main  intake  current,  and 
returned  at  once  to  the  main  return  airway.  To  accomplish 
this,  a  regulator  is  placed  at  the  intake  end  of  the  stables 
at  a,  Figs.  3  and  4,  the  return  end  of  the  stable  being  open 
to  the  return  airway  or  to  a  cross-cut  b  leading  to  the  return 
airway.  In  Fig.  3,  the  first  splitting,  made  a  short  distance 
frpm  the  foot  of  the  downcast  shaft  at  c,  divides  the  air-cur- 
rent into  two  primary  splits  that  pass,  respectively,  to  opposite 


FIG.  3 

sides  of  the  shaft,  each  split  being  again  divided  at  the 
mouth  of  the  first  pair  of  cross-entries  at  d.  The  figure 
shows  the  main  hoisting  shaft  as  an  upcast  and  hauling  as 
being  done  on  the  return  airways  of  the  mine.  The  division 
of  the  air  at  the  mouth  of  each  pair  of  cross-entries  requires 
air-crossings  at  e  and  /,  as  shown  in  the  figure  by  the 
cross-lines  at  these  points.  As  the  hauling  is  done  on  the 
return  air,  the  intake  air  must  travel  through  the  air  bridge, 
passing  over  or  under  the  haulage  road.  In  this  figure,  a 
door  regulator  is  shown  at  the  first  split  at  c,  and  box  reg- 
ulators at  a. 


30 


MINE  VENTILATION 


§14 


In  Fig.  4,  the  air-current  is  divided  at  the  foot  of  the  down- 
cast shaft  into  three  main  splits  c,  d,  and  e,  which  are  divided 
as  required  at  the  mouths  of  the  cross-entries.  Here,  also, 


FIG.  4 


hauling  is  done  on  the  return  air,  and  the  intake  air  must 
travel  over  the  air  bridge.  In  this  figure,  box  regulators  are 
used  near  the  mouths  of  the  return  airway  in  the  several  splits 


§14 


MINE  VENTILATION 


31 


where  necessary  to  accomplish  the  required  division  of  air. 
A  door  regulator  may  be  used,  if  necessary,  at  the  foot  of 
the  downcast  shaft. 

20.     Ventilation  of  a  Long- Wall  Mine:  Flat  Seam. 

The  general  disposition  of  the  air-current  in  the  ventilation 
of  a  long-wall  mine  is  shown  in  Fig.  5.  In  the  long-wall 
method  of  working,  all  the  coal  is  taken  out  and  no  pillars 
are  left  except  about  the  shaft.  The  face  at  which  the  coal 
is  mined  is  a  continuous  line  a,  a,  while  the  haulage  roads 
and  airways  are  passages  between  walls  of  loose  rock.  In 


FIG.  5 

the  case  illustrated,  the  hoisting  shaft  U  is  the  upcast,  haul- 
ing being  done  on  the  return  airway.  The  downcast  shaft  D 
is  located  in  the  shaft  pillar  and  the  mine  stable  is  between 
the  two  shafts.  The  air  is  divided  into  two  splits  at  the 
working  face  at  the  head  of  the  main  intake  airway  at  b, 
separate  currents  passing  to  the  right  and  left  around  the 
working  face,  and  returning  by  the  main  road  c  on  the 
opposite  side  of  the  shaft  to  the  shaft  bottom  at  the  foot  of 
the  upcast  or  hoisting  shaft.  By  this  arrangement,  the 
entire  working  face  is  ventilated  by  two  splits  only.  In  the 


32  MINE  VENTILATION  §14 

later  development  of  the  mine,  it  will  be  necessary,  however, 
to  divide  the  main  air-current  into  two  splits  at  the  foot  of 
the  downcast  shaft,  and  by  building  an  air  bridge  across  the 
main  haulage  road  at  the  shaft  bottom,  carry  one  of  these 
main  splits  directly  to  the  opposite  side  of  the  shaft.  Each 
of  these  main,  or  primary,  splits  will  then  be  again  split  at 
the  working  face,  passing  to  the  right  and  left  of  the  main 
road,  thus  dividing  the  circulation  in  the  mine  into  four  splits 
or  currents,  each  split  ventilating  a  quarter  of  the  entire 
circle  of  the  working  face.  In  this  arrangement,  the  two 
splits  from  the  opposite  sides  of  the  shaft  meet  at  the  heads 
of  the  main  haulage  roads  and  return  by  these  roads  to  the 
foot  of  the  upcast  shaft.  In  any  of  these  arrangements, 
curtains  or  canvas  doors  d  are  hung  at  the  head  of  each 
crossroad  and  working  place,  or  permanent  doors  are  located 
at  the  mouths  of  these  roads,  so  as  to  prevent  the  air  return- 
ing by  them  to  the  shaft  bottom.  In  any  case,  a  small  quan- 
tity of  air  is  allowed  to  traverse  these  roads  sufficient  for 
their  ventilation.  In  any  circulation  of  air,  it  is  important  to 
conduct  the  air,  as  far  as  practicable,  at  once  to  the  farthest 
point  inby  in  the  workings,  whence  it  is  allowed  to  traverse 
the  working  faces  on  its  return.  Long-wall  workings  are 
usually  more  easily  ventilated  than  room-and-pillar  workings, 
as  the  air-current  is  carried  directly  along  the  working  face 
where  it  is  most  required.  For  the  same  length  of  working 
face,  the  distance  traveled  by  the  air  is  less  in  long-wall 
work  than  in  room-and-pillar  work,  and  there  is  consequently 
less  loss  of  air  due  to  leaky  stoppings,  doors,  etc. 

21.  Ventilation  of  Inclined  Seams.— The  chief  fea- 
ture in  the  ventilation  of  an  inclined  seam  is  to  so  arrange 
the  air-current  that  the  circulation  of  the  air  through  the 
workings  shall  be  ascensional;  that  is,  the  air  circulating 
through  the  workings  shall  tend  to  rise.  This  is  not  always 
practicable,  but  where  it  can  be  accomplished  easily  there  is 
a  great  saving  in  expense  for  ventilation. 

Fig.  6  shows  a  mine  opened  by  a  pair  of  slopes  a  and  b 
driven  to  the  full  dip  of  the  seam.  Cross-entries  c  or 


14 


MINE  VENTILATION 


gangways  are  driven  on  the  strike  of  the  seam',  at  regular 
intervals  to  the  right  and  left  from  the  main  slope,  and  the 
coal  is  worked  by  driving  chambers  to  the  rise  of  these  gang- 


FIG.  6 

ways.  The  haulage  slope  a  is  shown  as  the  main  return  air- 
way, the  air  being  blown  into  the  mine  by  a  blower  fan  located 
at  the  top  of  a  shallow  shaft  d  connecting  with  the  intake 


34  MINE  VENTILATION  §14 

slope  b.  The  air  is  split  as  shown  at  the  mouth  e  of  the 
lower  one  of  each  pair  of  cross-entries  as  soon  as  the 
development  of  these  entries  warrants  the  expense  of  build- 
ing the  necessary  air  bridges.  Doors  are  used  for  deflecting 
the  main  current  into  the  gangways  until  such  time  as  the 
air  bridge  is  constructed.  The  current  is  not  divided  at  the 
last  two  pairs  of  cross-entries  that  have  just  been  turned, 
but  these  are  ventilated  with  the  same  current  traveling  in 
the  main  slope  airways,  doors  being  used  at  g  on  the  main 
and  return  slopes  to  deflect  the  air  to  the  faces  of  the 
entries. 

When  practicable,  the  ventilation  of  an  inclined  seam  is 
greatly  assisted  by  having  two  openings,  the  one  to  the  dip 
being  made  the  intake  opening,  and  the  one  to  the  rise  being 
the  discharge  opening.  In  this  arrangement,  the  circulation 
throughout . the  mine  is  truly  ascensional. 

22.  In  the  ventilation  of  a  steeply  inclined  thick  seam, 
the  airway  is  often  driven  close  to  the  roof,  as  shown  at  c  in 
Fig.  7  (d),  and  above  the  gangway^.  The  room  or  breast 
is  opened  by  a  narrow  chute  a  n  driven  up  the  pitch  from  the 
gangway  £-.  After  this  has  been  driven  up  a  certain  distance, 
depending  on  the  thickness  of  the  seam,  it  is  gradually 
widened  out  as  shown  at  k  to  the  width  of  a  room.  The  sec- 
tion (b}  shown  is  made  on  the  lines  Ik  and  z'/ and  the  plan  (a) 
is  made  on  the  line^^.  The  plan  therefore  does  not  show 
the  airway  c  nor  the  cross-cut  d.  The  breast  is  allowed  to 
fill  with  coal,  and  only  enough  is  drawn  out  through  the 
narrow  chute  a  at  the  bottom  to  keep  the  broken  coal  near 
the  face  so  that  the  men  may%  stand  on  it  while  mining. 
n  is  a  narrow  manway  so  that  the  men  can  work  about  the 
chute  and  control  the  flow  of  the  coal.  A  small  manway  m 
is  driven  up  from  the  gangway  £•  between  the  chutes,  and 
after  being  driven  for  a  certain  distance,  depending  on  the 
thickness  of  the  seam,  branches  s,  s  are  turned  off  this  man- 
way until  they  intersect  the  breast  on  each  side;  the  tops  of 
these  branches  s  connect  with  the  manways  w  along  each 
side  of  the  breast. 


§14 


MINE  VENTILATION 


35 


A  small  airway  d,  driven  between  the  airway  c  and  the  man- 
way  m,  serves  as  a  cross-cut  between  c  and  Awhile  they  are 
being  driven,  but  cross-cuts  are  also  necessary  between  the 
airways  and  the  gangway  £•  where  much  gas  is  given  off. 
The  small  cross-cut  d  and  the  airway  c  are  not  used  for  circu- 
lating the  air  ordinarily,  while  the  breasts  are  working;  but  if 
any  accident  takes  place  in  the  room  manway  w  by  which  the 
current  of  air  is  blocked,  the  air  may  be  conveyed  past  the 
room  through  the  airways  d  and  c. 
I 


P  (b) 

FIG.  7 

23.  Ventilation  of  Gaseous  Mines. — The  ventilation 
of  a  gaseous  mine  requires  such  an  arrangement  of  the  air- 
ways as  will  furnish  an  abundance  of  air,  and  give  the  best 
possible  control  over  the  ventilating  current  and  furnish  the 
largest  area  for  the  return  currents.  For  this  reason,  the 
entries  are  often  driven  three  abreast,  an  arrangement  called 
the  triple-entry  system.  In  Fig.  8,  the  main  entries  a,  b, 
and  c  are  shown  as  triple  entries,  while  the  cross-entries  d 
and  e  are  driven  in  pairs  and  known  as  double  entries. 


36 


MINE  VENTILATION 


§14 


In  the  triple-entry  system,  the  middle  entry  of  the  three 
should  be  made  the  intake  entry  and  haulage  road,  while  the 
two  side  entries  flanking  the  haulage  road  form  the  return 
for  each  side  of  the  mine,  respectively. 

In  the  figure,  the  air  is  shown  as  split  at  /,  each  pair  of 
cross-entries  receiving  a  separate  split.  Air  bridges  g  carry 
the  return  air  over  the  haulage  roads  leading  from  the  side 
entries.  Where  the  cross-entries  are  long  and  the  mine  very 
gaseous,  these  also  are  driven  as  triple  entries.  The  top  of 
the  figure  is  toward  the  mine  opening. 


In  a  gaseous  mine,  the  ventilation  should  be  so  arranged 
that  the  hauling  can  be  done  on  the  intake  air-course,  as  this 
is  safer,  since  it  avoids  the  danger  of  the  ignition  of  gas  by 
the  lamps  of  the  drivers.  This  will  require  the  use  of  an 
exhaust  fan  instead  of  a  blower,  in  order  to  avoid  the 
necessity  for  doors  on  the  main  haulage  road  at  the  foot  of 
the  shaft  or  slope,  or  at  the  mouth  of  a  drift,  as  the  case 
may  be.  Hauling  on  the  intake  has  the  following  dis- 
advantages: The  intake  air  is  laden  with  the  dust  of  the 
haulage  road,  which  is  carried  into  and  deposited  in  the 
workings.  The  movement  of  the  loaded  cars  against 


§14  MINE  VENTILATION  37 

the  air-current  obstructs  the  circulation  more  than  do  the 
empty  cars  moving  with  the  return  current.  Any  refuse 
accumulating  on  the  haulage  road  vitiates  the  air-current 
before  it  reaches  the  working  face.  The  coal  that  falls  from 
the  cars  along  the  roadways  and  is  crushed  to  a  fine  dust 
is  more  an  element  of  danger  on  an  intake  airway  than  on 
the  return,  in  case  of  a  dust  explosion  in  the  mine.  For 
these  reasons,  it  is  better  in  the  absence  of  gas  to  make  the 
haulage  road  the  return  airway  of  the  mine. 

The  number  of  doors  used  in  connection  with  the  ventila- 
tion of  a  mine  should  be  as  small  as  possible,  as  doors  on 
haulage  roads  obstruct  the  roads,  increase  the  expense  for 
trappers,  or  door  tenders,  and  also  increase  the  danger 
of  explosions,  since  if  a  door  is  left  open  the  entire  air- 
current  may  be  disarranged.  Again,  in  case  of  an  explosion, 
if  a  door  is  destroyed  the  entire  air-current  of  the  mine  may 
be  disarranged  until  the  door  can  be  restored.  Hence, 
wherever  possible,  the  plan  of  ventilation  should  be  such 
that  overcasts  may  be  used  and  doors  avoided.  A  gaseous 
mine  should  be  ventilated  in  separate  districts  as  far  as 
possible,  so  as  to  confine  the  effects  of  an  explosion  to  a 
single  district.  

MEANS  FOR  VENTILATING  MINES  • 


NATURAL,    VENTILATION 

24.  Natural  ventilation  means  the  production  of  an 
air-current  without  the  use  of  any  form  of  ventilator.  The 
principle  on  which  all  natural  ventilation  depends  is  the  dif- 
ference in  weight  between  two  columns  of  air  of  different 
densities.  This  difference  in  weight  produces  a  flow  of  air 
from  the  heavier  to  the  lighter  air  column. 

The  pressure  of  the  atmosphere  on  the  surface  of  the  earth 
is  due  to  the  weight  of  the  air.  The  pressure  on  each  square 
inch  of  surface,  at  sea  level  (14.7  pounds)  is  equal  to  the 
weight  of  a  column  of  air  whose  base  is  1  square  inch  and 
whose  height  is  the  height  of  the  atmosphere.  The  pressure 


38 


MINE  VENTILATION 


§14 


on  each  square  foot  of  surface  (2,116.8  pounds)  is  equal  to 
the  weight  of  a  column  of  air  whose  base  is  1  square  foot 
and  whose  height  is  that  of  the  atmosphere. 

25.  Air  Columns. — An  air  column  in  ventilation  is  a 
column  of  air  having  a  base  of  1  square  unit  (usually  1  square 

A JF          foot)   and  a  height  equal 

to  the  height  of  the  air 
considered.  Thus,  the 
height  of  an  air  column  in 
a  shaft  is  the  depth  of  the 
shaft;  the  height  of  the  air 
FlG-9  column  in  a  slope  is  the 

vertical  height  of  the  slope.  In  Fig.  9,  the  depth  of  the 
shaft  A  B  is  equal  to  the  vertical  height  of  the  slope  C E\ 
hence,  in  this  case,  the  height  of  air  column  in  the  shaft  is 
equal  to  that  in  the  slope.  In  comparing  the  weights  of 
these  two  air  columns,  it  is  evident  that  it  is  not  necessary 
to  consider  the  air  columns  extending  up  through  the  atmos- 
phere above  A  and  E,  since  they  are  alike  in  each  case,  and 
their  weights  will,  there- 
fore, balance  each  other. 

26.  How    Air    Col- 
umns   Produce    Air- 
Currents. — As  was  fully 
explained  in  Mine  Ventila- 
tion, Part  1,  when  the  two 
ends    of    an    airway    a  £, 
Fig.  10,  are  acted  on  by  air 
columns  ac  and  bd  of  dif- 
ferent densities  or  weights, 
the  air  at  the  ends  of  the 
airway'  is  subjected  to  dif- 
ferent pressures  and  will,  FIG.  10 

therefore,  move  in  a  direction  from  the  greater  pressure 
toward  the  lesser  pressure,  as  shown  by  the  arrows.  The 
difference  between  these  two  pressures,  or  the  weights  of 
the  two  air  columns,  is  the  unit  of  ventilating  pressure  / 


§14  MINE  VENTILATION  39 

for  the  same  unit  of  cross-section,  which  is  usually  taken  as 
1  square  foot.  The  total  pressure  producing  circulation  here 
also,  is  equal  to  the  entire  pressure/ a  exerted  on  the  sectional 
area  of  the  airway.  In  natural  ventilation,  the  ventilating 
pressure  pa  is  dependent  on  the  difference  of  the  weights  of 
the  two  air  columns  and  the  sectional  area  of  the  airway. 

Suppose,  for  example,  a  mine  to  be  ventilated  by  two 
shafts,  each  having  a  depth  of  500  feet.  The  average  tem- 
perature of  the  downcast  shaft  is  assumed  to  be  32°  F.,  and 
the  average  temperature  of  the  upcast  shaft  60°  F.,  and  the 
barometer  to  read  30  inches.  To  calculate  the  ventilating 
pressure  due  to  the  difference  between  the  weights  of  these 
two  air  columns,  it  is  necessary  to  first  find  the  weight  w^  of 
1  cubic  foot  of  air  in  the  downcast,  and  the  weight  w*  of 
1  cubic  foot  of  air  in  the  upcast  by  the  formula, 

1.3273  ff  (1) 

460  +  / 

in  which  w  =  weight  of  1  cubic  foot  of  air  at  a  tempera- 
ture /  and  a  barometric  pressure  B\ 
B  =  barometric  pressure,  in  inches  of  mercury; 
/  =  temperature  of  air,  in  degrees  F. 

-^H-°  =  -08093  — 

and,  w>  =     '         .*—  =  .07657  pound 


Multiplying  each  of  these  weights,  in  turn,  by  the  depth  D 
of  the  shaft  gives  the  total  weight  of  the  downcast  and  upcast 
air  columns;  thus, 

Weight  of  downcast  column, 

D  TV*  =  500  X  .08093  =  40.465  pounds 
Weight  of  upcast  column, 

D  wt  =  500  X  .07657  =  38.285  pounds 
Difference,     2.180  pounds 

The  weight  W  of  any  air  column  Dw  is  therefore  given 
by  the  formula 


40  MINE  VENTILATION  §14 

The  difference  between  the  weights  of  these  two  air 
columns  is  the  unit  of  ventilating  pressure,  which  may  also 
be  found  thus: 

D(wt-w,)  =  500  (.08093  -  .07657)  =  2.180  pounds 

Expressed  as  a  formula,  this  is 

p  =  D(wl-w,)  (3) 

in  which  p  =  unit  of  ventilating  pressure,   in   pounds   per 

square  foot; 

D  =  depth  of  shaft,  in  feet; 
Wi  =  weight,  in  pounds,  of  1  cubic  foot  of  air  in 

downcast; 
w,  =  weight,  in  pounds,  of  1  cubic  foot  of  air  in 

upcast. 

By  substituting,  in  formula  3,  the  expressions  for  wv 
and  w,  obtained  from  formula  1, 

,-71.3273  B  _  1.3273ff\ 
\460°  +  A       460  +  tj 


in  which  the  letters  p,  D,  and  B  have  the  same  significance 
as  in  formula  3  and  /t  is  the  average  temperature  in  down- 
cast shaft  and  /„  is  the  average  temperature  in  upcast  shaft. 

27.     Motive   Column.  —  The  term   motive   column  is 

often  used  to  express  the  unit  of  ventilating  pressure  in  mine 
ventilation.  It  is  an  imaginary  column  of  air  having  a  base 
of  1  square  foot  and  a  height  such  that  the  weight  of  the  air 
column  will  be  equal  to  the  unit  of  ventilating  pressure,  or 
the  pressure  per  square  foot  in  the  airway 

Since  the  motive  column  is  an  imaginary  column  of  air  of 
such  height  that  its  weight  will  produce  a  certain  pressure,  it 
may  be  assumed  to  consist  of  air  of  any  given  density.  For 
the  same  pressure,  the  height  of  the  motive  column  will  be 
greater  or  less,  according  to  the  density  of  the  air.  For 


§14  MINE  VENTILATION  41 

example,  for  the  same  pressure,  the  motive  column  of 
upcast  air  will  have  a  greater  height  than  that  of  downcast 
air,  because  the  upcast  air  is  lighter  and  requires  a  larger 
amount  to  produce  the  same  pressure.  Although  the  motive 
column  is  usually  now  given  in  terms  of  the  downcast  air 
column,  some  writers  give  it  in  terms  of  the  upcast.  This 
gives  rise  to  two  formulas  for  motive  column  and  unless 
this  is  understood  confusion  is  occasioned.  To  make  this 
clear,  assume  a  mine  ventilated  by  two  shafts,  each  being 
600  feet  deep,  the  upcast  having  an  average  temperature  of 
150°  F.,  and  the  downcast  an  average  temperature  of  40°  F. 
The  weights  of  these  two  shaft  columns  are  as  follows,  using 
formula  2,  Art.  26. 

Downcast  column,  W  =  600  X  1-3273  x  3Q  =  47.7828  pounds 

460  +  40 

Upcast  column,  W  =  600  X  1-3273  x  3Q  =  39.1662  pounds 

4oU  ~r~  J.OU 

The  unit  of  ventilating  pressure  in  this  case  is  then 
47.7828  -  39.1662  =  8.6166  pounds. 

The  weight  of  1  cubic  foot  of  the  downcast  air  is  then 
.079638  pound;  and  the  weight  of  1  cubic  foot  of  the  upcast 
air  is  .065277  pound.  The  heights  of  motive  column  of 
downcast  and  upcast  air,  respectively,  that  alone  would  pro- 
duce this  pressure  are  as  follows: 

Motive  column,  downcast  air,  8.6166  -^  .079638  =  108.2  feet, 
nearly. 

Motive  column,  upcast  air,  8.6166  -4-  .065277  =  132.0  feet. 

Both  of  these  motive  columns  produce  the  same  unit  pres- 
sure, which  is  found  by  multiplying  the  height  of  the  motive 
column  by  the  weight  of  1  cubic  foot  of  the  air  of  which  it 
is  composed.  Thus,  the  unit  of  ventilating  pressure  in  each 
case  is  as  follows: 

t)  =  108.2  x  .079638  =  8.616+; 
or,  A=  132.0  X  .065277  =  8.616  + 

Unless  otherwise  stated,  the  motive  column  will  always  be 
given  in  terms  of  the  downcast  air.  The  downcast  air  is 
always  the  heavier,  and  as  shown  in  Fig.  11,  when  the  upcast 
is  heated  by  a  furnace,  as  will  be  explained  in  detail  later,  a 


42 


MINE  VENTILATION 


§14 


portion  only  of  the  downcast  column  is  necessary  to  balance 
the  entire  weight  of  the  upcast  column.  The  remainder 
of  the  downcast  column,  or  the  excess  of  weight  of  the 

downcast  air,  will  then  rep- 
resent the  motive  column 
of  downcast  air.  If  the 
motive  column  were  esti- 
mated in  upcast  air,  it 
would  not  be  possible  to 
illustrate  it  in  this  manner 
as  it  would  then  be  purely 
an  imaginary  column. 

To  obtain  the  height  of 
the  motive  column  in 
terms  of  the  downcast  air 
divide  the  unit  of  venti- 
lating pressure  as  found 
in  Art.  26,  by  the  weight 


of  1  cubic  foot  of  downcast  air;  thus, 
M  =  D  (1.3273: 


or,  M  =  D(  1.3273  X 


(460  +  /,)  (460  +  /,) 
*,-/, 


1.3273  X  B 
460  +  /t 
460 +  /, 


and, 


M  =  D 


(460  +  /J  (460  +  /J      1.3273  X  B 


(1) 


460  +  /, 

In  like  manner,  the  height  of  motive  column  in  terms  of 
the  upcast  air  is  found  by  dividing  the  unit  of  ventilating 
pressure  given  above,  by  1  cubic  foot  of  the  upcast  air, 
giving  the  formula, 

«-D&h       (2) 

To  show  the  application  of  these  formulas,  the  height  of 
motive  column,  in  terms  of  the  downcast  and  the  upcast  air, 
respectively,  in  the  example  given  in  Art.  27,  may  be  cal- 
culated directly  by  substituting  the  values  D  =  600  feet, 
A  =  40°  F.,  /2  =  150°  F.,  in  turn,  in  each  of  the  above 
formulas;  thus, 


§14  MINE  VENTILATION  43 

Motive    column   (downcast   air)    M  =  600  — — ;   or, 

M  =  600  X  i-Hr  =  108+  feet;   motive  column  (upcast  air) 

M  =  600  }^  ~  ^;  or,  M  =  600  X  ti%  =  132  feet.    The  cal- 
460  +  40 

culation  by  these  formulas  is  thus  seen  to  be  much  shorter 
than  by  the  previous  method. 

28.  When  a  ventilating  current  is  due  to  the  difference 
in  'weight  of  the  downcast  and  upcast  air  columns,  it  is 
important  to  remember  that,  for  the  same  temperatures,  the 
unit  of  ventilating  pressure  p  due  to  these  air  columns 
remains  constant;  and  for  the  same  sectional  area  a  of  the 
airway,  the  total  pressure  p  a  producing  ventilation,  or  the 
ventilating  pressure,  is  constant.  Hence,  in  considering  such 
circulations,  the  mine  resistance  (pa  =  ksv*)  is  a  constant, 
and  the  velocity  of  the  air  passing  through  the  mine 
decreases  with  any  increase  in  the  rubbing  surface. 

Or,  again,  the  ventilating  pressure^ a  being  constant,  any 
increase  or  decrease  of  the  velocity  v,  due  to  a  change  in  the 
rubbing  surface  of  the  airway,  results  in  a  corresponding 
increase  or  decrease  in  the  power  on  the  air.  In  other 
words,  the  sectional  area  of  the  airway  and  the  ventilating 
pressure  both  being  constant,  any  increase  in  the  length, 
and,  consequently,  in  the  rubbing  surface  of  the  airway,  pro- 
duces a  decrease  in  the  power  on  the  air,  and,  vice  versa,  any 
decrease  in  the  length  produces  an  increase  in  the  power  on 
the  air.  In  this  respect,  there  is  an  important  difference 
between  the  consideration  of  air  columns  in  natural  or  in 
furnace  ventilation  and  any  form  of  fan  ventilation,  since, 
with  fans,  the  power  delivered  to  the  fan  shaft  remains  con- 
stant and  the  power  on  the  air  is  also  practically  constant 
for  any  given  case.  

EXAMPLES    FOB    PRACTICE 

1.  The  downcast  shaft  of  a  mine  is  437  feet  deep,  the  mean  baro- 
metric pressure  is  30.25  inches,  and  the  mean  temperature  of  the  air 
in  the  shaft  is  67°  F.;  what  is  the  weight  of  a  column  of  air  in  this 
shaft,  having  a  base  of  1  square  foot?  Ans.  33.2939  Ib. 

145—18 


44  MINE  VENTILATION  §14 

2.  The  downcast  shaft  of  a  mine  is  1,147  feet  deep,  the  mean  baro- 
metric pressure  is  29.9  inches,  and  the  mean  temperature  of  the  air  in 
the  shaft  is  50°  F.;  what  is  the  weight  of  a  column  of  air  in  this  shaft, 
having  a  base  of  1  square  foot?  Ans.  89.2552  Ib. 

3.  The  upcast  shaft  of  a  mine  is  347  feet  deep,  the  mean  barometric 
pressure  is  30  inches,  and  the  mean  temperature  of  the  air  in  the  shaft 
is  187°  F.;  what  is  the  weight  of  a  column  of  air  in  this  shaft,  having 
a  base  of  1  square  foot?  Ans.  21.35578  Ib. 

4.  The  upcast  shaft  of  a  mine  is  1,170  feet  deep,  the  mean  baro- 
metric pressure  is  29.5  inches,  and  the  mean  temperature  of  the  air  in 
the  shaft  is  160°  F.;  what  is  the  weight  of  a  column  of  air  in  this  shaft, 
having  a  base  of  1  square  foot?  Ans.  73.8899  Ib. 

5.  The  ventilating  shafts  of  a  mine  are  each  950  feet  deep,  the  tem- 
perature of  the  downcast  column   is   60°    F.,    that  of  the  upcast  is 
230°  F.,  and  the  barometric  pressure  is  30  inches,     (a)  What  is  the 
length  of  the  motive  column  in  terms  of  the  downcast  air?     (b)  What 
is  the  difference  in  the  weights  of  the  ventilating  columns  per  square 
foot  of  area?  .       /  (a)  234+  ft. 

Ans-\(£)  17.923  Ib. 

6.  The  ventilating  shafts  of  a  mine  are  each  760  feet  deep,  the 
temperature  of  the  downcast  is  52°  F.,  and  that  of  the  upcast  is  280°  F. 
and  the  barometric  pressure  is  30  inches,     (a)  What  is  the  length  of 
the  motive  column  in  terms  of  the  upcast  air?     (b)  What  is  the  differ- 
ence in  the  weights  of  the  ventilating  columns  per  square  foot  of  area? 

A       f  (a)  338+  ft. 
Ans'l(*)   18.2  Ib. 


29.  Average  Temperatures  of  Air  Columns. — Where 
a  considerable  current  of  air  is  passing  into  a  mine,  it  will 
require  a  very  deep  shaft  to  materially  increase  the  tempera- 
ture of  the  intake  air  above  that  of  the  outside  atmosphere. 
For  this  reason,  it  is  rarely  necessary  to  consider  more  than 
two  temperatures  in  calculating  the  pressure  producing  the 
circulation  of  air;  these  are  the  average  downcast  and  upcast 
temperatures.  The  average  downcast  temperature  will  rarely 
exceed  to  any  appreciable  extent  the  temperature  of  the  out- 
side air,  except  in  very  deep  shafts  or  where  the  downcast 
air  is  warmed  by  steam  pipes  or  other  artificial  means. 

The  temperature  of  an  upcast  column  is  subject  to  more 
variation  than  that  of  the  downcast  column,  and  the  fall  of 
temperature  in  the  upcast  is  often  much  greater  than  the  rise 


§14 


MINE  VENTILATION 


45 


of  temperature  in  the  downcast,  since  there  are  more  agen- 
cies acting  to  cool  the  upcast  current.  The  amount  of 
cooling  will  depend  largely  on  the  difference  between  the 
temperature  at  the  bottom  of  the  upcast  and  the  temperature 
of  the  outside  air.  Where  this  difference  is  considerable, 
as  in  furnace  ventilation,  the  amount  of  cooling  is  increased. 
The  influence  of  moisture  in  a  deep  upcast  shaft  is  to  trans- 
fer the  heat  from  the  bottom  to  the  upper  portion  of  the 
shaft.  This  is  due  to  the  evaporation  of  the  water  and  the 
consequent  absorption  of  heat  in  the  lower  portion  of 
the  shaft,  and  its  condensation  and  the  consequent  develop- 
ment of  heat  in  the  upper  portion  of  the  shaft.  The  evapo- 
ration of  the  water  in  the  lower  portion  of  the  shaft  is, 
however,  always  greater  than  the  condensation  in  the  upper 
portion,  as  by  far  the  larger  portion  of  the  water  evaporated 
is  carried  away  in  the  air.  Occasionally,  in  a  fan  drift  at 
the  top  of  an  upcast  shaft,  the  condensation  of  the  water 
from  the  air-current  is  like  the  downpour  of  a.  heavy  rain. 
The  average  temperature  of  the  upcast  can  be  accurately 
estimated  only  after  long  experience. 

30.     Influence  of  Seasons  on  Mine  Ventilation. — In 

the  winter  season,  the  outside  air  is  generally  colder  than  the 
mine  air.  This  has  the  effect  of  reducing  the  temperature 
of  the  intake  air,  and  increasing  its  weight  above  that  of  the 


FIG.  12 


return  air  of  the  mine.  In  the  summer  season,  the  outside 
air  being  generally  warmer  than  the  air  of  the  mine,  the 
temperature  of  the  intake  is  increased,  and  may  be  higher 
than  the  temperature  of  the  return  air  of  the  mine  while  the 


46  MINE  VENTILATION  §14 

weight  is  decreased.  Hence,  the  influence  of  the  winter 
season  is  to  assist  the  circulation  in  the  mine  wherever  the 
intake  passes  downwards  and  the  return  air  upwards,  and  to 
oppose  all  circulations  where  the  intake  passes  to  the  rise 
and  returns  to  the  dip.  The  effect  of  the  summer  season  is 
the  reverse  of  this. 

In  a  drift  mine  connected  to  a  shaft,  as  shown  in  Fig.  12, 
and  ventilated  by  natural  means  only,  the  circulation  may  be 
reversed  in  the  summer  from  what  it  is  in  the  winter  season 
due  to  the  differences  in  temperature  between  the  min°.  air 
and  the  outside  air.  In  summer,  a  cold  and  therefore  heavier 
shaft  column  of  air  is  opposed  to  a  hot  outside  air  column 
producing  a  current  down  the  shaft  and  out  the  drift;  in 
winter,  a  hot  and  therefore  lighter  shaft  column  is  opposed 
to  a  cold  outside  column  producing  a  current  into  the  drift 
and  up  the  shaft.  Thus  the  shaft  is  a  downcast  in  sum- 
mer and  an  upcast  in  winter.  At  certain  periods  of  the 
spring  and  fall,  when  there  is  little  difference  in  temperature 
between  the  mine  and  outside  air,  the  ventilation  in  such 
mines  will  be  very  poor.  Where  artificial  means  of  ventila- 
tion are  used,  the  effect  produced  by  the  change  of  the 
seasons  will  depend  on  the  character  of  the  mine  and  the 
system  of  ventilation  employed.  If  an  exhaust  fan  be  placed 
at  the  top  of  the  shaft  shown  in  Fig.  12,  the  natural  ventila- 
tion will  assist  the  artificial  ventilation  of  this  mine  in  winter 
and  oppose  it  in  summer.  If  a  blower  fan  be  placed  at  the 
top  of  the  shaft,  the  natural  ventilation  will  assist  the  arti- 
ficial ventilation  in  summer  and  oppose  it  in  winter.  In  the 
use  of  the  blower  fan,  the  temperature  of  the  air  in  the  fan 
shaft  is  very  nearly  uniform  throughout  the  entire  depth  of 
the  shaft. 

The  effect  of  the  changes  of  seasons  on  the  ventilation 
produced  by  a  blower  fan  will  be  very  slight,  however,  for 
such  a  fan  fills  the  downcast  shaft  with  air  at  a  temperature 
that  varies  but  slightly  from  the  temperature  of  the  outside 
air  and  the  shaft  air  column  is  very  nearly  balanced  by  the 
outside  air  column;  this  is  not  the  case  when  an  exhaust  fan 
is  used. 


§14 


MINE  VENTILATION 


47 


FIG.  13 


31.  In  the  ventilating  of  a  mine  having  two  openings,  the 
one  an  intake  and  the  other  a  discharge  opening  at  practically 
the  same  level,  as  shown  in  Fig.  13,  artificial  means  must 
be  employed  to  produce  the  circulation.  In  this  case,  there 
is  no  natural  ventilation 
until  an  air-current  is  estab- 
lished, by  a  furnace  or  ven- 
tilator, but  if  the  mine  is 
operated  through  a  shaft 
or  slope  and  there  is  a  dif- 
ference between  the  tem- 
perature of  the  outside  air 
and  that  of  the  mine  air,  a 
shaft  air  column  or  a  slope 
column  forms  in  the  shaft  or  the  slope  immediately  on  a  cur- 
rent being  artificially  established.  The  effect  of  the  change 
of  the  seasons  in  this  case  is  the  same  whether  an  exhaust 
or  a  blower  fan  is  used.  In  the  winter  the  natural  shaft 
column  will  assist  the  artificial  ventilation  produced  by 
either  an  exhaust  or  a  blower  fan,  and  in  the  summer  the 
natural  shaft  column  will  oppose  the  artificial  ventilation 

produced    by    either    of    these 

ventilators. 

32.  In  a  slope  or  shaft  mine 
at  which  the  intake  and  dis- 
charge openings  of  the  mine  are 
at  different  levels  as  shown  in 
Fig.  14,  there  is  always  a  nat- 
ural outside  air  column  having 
a  height  ED  equal  to  the  dif- 
ference in  vertical  distance  be- 
tween the  tops  of  these  two 
openings,  and  this  air  column 
will  produce  a  natural  circulation  of  air  in  the  mine  in  exactly 
the  same  way  as  was  explained  in  connection  with  the  drift 
mine  shown  in  Fig.  12.  The  air  column  EC  is  made  up 
of  two  parts — the  column  of  air  DC  inside  the  mine  and 


Fiq,  14 


48  MINE  VENTILATION  §14 

column  DE  outside  the  mine — while  the  column  A  B  is  wholly 
inside  the  mine.  The  effect  of  this  natural  air  column  ED 
in  the  absence  of  any  artificial  means  of  ventilation  is  to 
make  the  higher  opening  of  the  mine  an  intake  or  down- 
cast in  the  summer  and  a  discharge  or  upcast  in  the  winter, 
in  the  same  manner  as  was  explained  with  regard  to  a  drift 
mine  ventilated  by  a  shaft  and  shown  in  Fig.  12. 

The  effect  of  artificial  ventilation  applied  to  this  mine, 
whatever  its  arrangement,  would  be  to  fill  the  downcast  shaft 
with  the  hot  outside  air  in  the  summer  and  with  the  cold 
outside  air  in  the  winter,  which  would  produce  an  unfavorable 
motive  column  in  the  summer,  but  a  favorable  motive  column 
in  the  winter.  In  other  words,  in  this  case,  the  change  of 
the  seasons  would  oppose  the  artificial  ventilation  in  the 
summer  and  assist  it  in  the  winter.  This  influence  of  the 
seasons  on  the  artificial  ventilation  of  shaft  and  slope  mines 
where  the  mine  openings  are  at  different  elevations  is,  there- 
fore, practically  the  same  as  in  the  case  of  shaft  or  slope 
mines  where  the  openings  are  at  the  same  level;  because,  if 
the  higher  opening  is  the  intake,  the  natural  outside  air 
column  is  practically  destroyed  as  soon  as  artificial  ventila- 
tion is  established,  owing  to  the  downcast  shaft  column  then 
having  practically  the  same  temperature  as  the  outside  air; 
if  the  lower  opening  be  the  intake,  the  outside  air  column 
becomes  the  extension  of  the  downcast  shaft  column  which 
also  has  practically  the  same  temperature  as  the  outside  air. 

33.  Rise  and  Dip  Workings. — It  is  a  matter  of  com- 
mon observation  that  rise  workings  are,  in  general,  more 
difficult  to  ventilate  than  dip  workings.  The  reason  for  this 
is  that  the  intake  current  is  usually  cooler  than  the  return 
current,  and  there  is  thus  formed  a  negative  air  column 
opposing  the  circulation  in  rise  workings  and  a  positive  air 
column  assisting  the  circulation  in  dip  workings.  The 
influence  of  dips  and  rises  in  mine  workings  is  often  a 
powerful  one,  at  times  completely  controlling  the  ventilation 
of  the  workings.  On  this  account,  seams  having  any  con- 
siderable inclination  should  be  ventilated  as  far  as  practicable 


§14  MINE  VENTILATION  49 

so  that  the  intake  air  will  flow  to  the  dip  and  the  return  to 
the  rise.  When  it  is  practicable  to  so  arrange  the  ventila- 
tion of  a  mine,  the  air  should  be  taken  into  the  mine  at  its 
lowest  point  and  discharged  at  its  uppermost  point,  so  that 
the  circulation  of  the  mine  may  be  ascensional. 

34.  Density  of  Air  Columns. — Whatever  affects  the 
density  of  the  air  affects  the  weight  of  the  air  column;  tem- 
perature, pressure,  moisture,  presence  of  gases,  all  affect  the 
weight  of  the  air  column  to  a  greater  or  less  degree.     In 
very  accurate  calculations,  all  these  factors  might  be  con- 
sidered in  determining    the  weights  of   the  respective  air 
columns,  but   ordinarily   only    the    temperature  of   the   air 
column  and  the  barometric  pressure  are  considered.     The 
effect  of  moisture  in  this  respect  is  very   slight,   but  the 
presence  of  any  considerable  amount  of  carbon-dioxide  gas, 
or  of  carbureted-hydrogen  gas  in  the  upcast  current,  or  in 
the  return  current  of  an  inclined  seam,  may  affect  the  air 
column  to  an  extent  that  will  depend  on  the  amount  of  either 
gas  present. 

35.  Ventilation  of  a  Shaft  During  Sinking. — There 
is  not  much  difficulty  experienced  from  the  lack  of  air  in 
sinking  a  shaft  until  a  depth  of  15  or  20  yards  is  reached, 
depending    somewhat   on  the   size   of   the  shaft.     When  it 
becomes  necessary  to  provide  for  the  ventilation  of  the  shaft, 
it  should  be  divided  into  two  compartments  by  an  air-tight 
partition,  which  may  be  temporary  or  permanent.     This  par- 
tition should  extend  from  the  top  of  the  shaft  to  within  3  or 
4  yards  of  the  bottom,  and,  in  general,  the  natural  heat  pro- 
duced by  the  workmen  at  the  bottom  of  the  shaft  will  cause 
a  current  of  air  to  descend  on  one  side  of  this  partition  and 
ascend  on  the  other.     This  movement  of  the  air  may  be 
assisted  by  providing  a  stack  of  common  12-foot  or  16-foot 
boards  at  the   top  of  the  air  compartment  or  manway,  as 
shown  in  Fig.  15. 

When  a  depth  is  reached  at  which  the  natural  ventilation 
thus  provided  is  insufficient,  a  small  hand  blower  may  be 
used  at  the  surface  of  the  shaft,  or  a  fire-basket  maybe  used 


50 


MINE  VENTILATION 


§14 


consisting  of  an  iron  grating  in  the  form  of  a  basket  in  which 
a  bed  of  coals  or  fire  may  be  placed,  and  which  is  then  lowered 
into  the  shaft.  Sometimes,  a  steam  pipe  is  conducted  down 
the  shaft,  and  a  steam  jet  is  used  to  create  an  upward  current 


of  air.  When  compressed  air  or  steam  is  used  for  the  opera- 
tion of  the  drills  at  the  bottom  of  the  shaft,  there  is  generally 
no  need  for  further  ventilation  than  that  produced  by  the 
exhaust  air  or  steam.  

FURNACE    VENTILATION 

36.  Furnace  ventilation  depends  on  exactly  the  same 
principles  as  natural  ventilation  and  all  that  has  been  said 
with  respect  to  air  columns  in  natural  ventilation  applies 
alike  to  furnace  ventilation.  The  purpose  of  a  mine  furnace, 
as  illustrated  in  Fig.  11,  is  to  heat  the  upcast  column  to 
a  much  higher  temperature  than  is  possible  by  the  natural 
heat  of  the  mine.  The  high  temperature  produced  by  the 
furnace  greatly  reduces  the  weight  of  the  upcast  column  and 
therefore  increases  the  unit  of  ventilating  pressure.  The 
chief  difference,  therefore,  between  natural  ventilation  and 


§14  MINE  VENTILATION  51 

furnace  ventilation  is  that  in  the  former  the  air  is  heated  by 
natural  means  and  in  the  latter  by  artificial. 

3T;  Construction  of  a  Mine  Furnace. — As  the  fur- 
nace is  still  used  in  many  localities  for  the  ventilation  of 
mines  where  the  output  does  not  justify  the  erection  of  a 
ventilating  fan,  its  construction  and  use  should  be  known. 

Fig.  14  illustrates  a  good  type  of  furnace.  It  is  important 
in  building  a  furnace  to  construct  it  so  as  to  keep  the  exces- 
sive heat  of  the  fire  from  the  rib  coal  at  each  side,  and  from 
the  roof  rock  above.  In  Fig.  16,  /  is  the  rib  coal;  p,  the  ash- 


FiG.  16 

pit;  g,  the  bearing  bar  or  front  fire-grate  girder;  and  b  are  the 
grate  bars  that  form  the  fire-grate  surface.  The  furnace 
arch  a  is  generally  semicircular  and  double,  the  height  from 
the  grate  bars  to  the  under  surface  of  the  arch  being  gener- 
ally li  times  the  width  of  the  fire-grate.  The  side  drifts  d 
and  the  annular  space  above  the  fire-arch  a  keep  the  heat 
from  the  coal  and  the  roof.  Ribs  of  brick  c  separate  the 
two  arches  and  serve  to  keep  the  air  space  open  so  that  a 
current  of  air  may  freely  pass  through  it  and  keep  the  heat 
from  the  roof.  The  importance  of  this  arrangement  lies 
in  the  fact  that  in  cases  where  the  roof  contains  water,  the 


52 


MINE  VENTILATION 


§14 


Ma/'n  Info/re  Atiau/aae 


P/an 


fire-arch  a,  if  not  so  protected,  is  continually  buckling  with 
the  pressure  produced  by  the  steam  formed  in  the  roof 
strata,  and  this  causes  the  roof  to  break  and  fall. 

38.  The  Dumb  Drift. — What  is  called  a  dumb  drift 
in  furnace  ventilation  is  a  short  connection  driven  from  a 
point  30  or  40  yards  back  from  the  foot  of  the  furnace  shaft 
upwards  through  the  roof  strata  to  intersect  the  shaft  at  a 
sufficient  height  to  avoid  the  ignition  of  the  gases  in  the 
return  air-current  by  the  flame  of  the  furnace.  This  con- 
nection, called  a  dumb  drift,  may  be  driven  in  any  manner 

most  convenient  and 


best  adapted  to  the 
conditions  existing  in 
any  particular  case. 
It  is  not  ordinarily 
considered  good  prac- 
tice to  ventilate  a  gas- 
eous mine  by  means 
of  a  furnace,  and 
the  practice  is  fast 
becoming  obsolete. 
When  a  dumb  drift  is 
used,  a  substantial 
air-tight  stopping  b, 
Fig.  17,  is  built  just 
outside  of  the  point 
where  the  dumb  drift  leaves  the  entry,  its  purpose  being  to 
deflect  the  return  air-current  into  the  drift  by  which  it  is  con- 
ducted into  the  upcast  or  furnace  shaft  at  a  suitable  height 
above  the  bottom  of  the  shaft.  The  furnace  /  is  built  10  or 
15  yards  from  the  foot  of  the  shaft,  and  between  the  stopping  b 
and  the  furnace  /a  cross-cut  or  heading  a  is  driven  to  connect 
the  furnace  drift  with  the  main  intake  airway.  In  this  cross- 
heading,  two  regulator  doors  are  built  to  prevent  the  short- 
circuiting  of  the  intake  current  at  this  point.  A  small  split  of 
air  is  allowed  to  pass  through  the  regulators  in  these  doors, 
sufficient  to  feed  the  furnace  with  fresh  air.  By  means  of 


§14  MINE  VENTILATION  53 

this  arrangement,  the  furnace  shaft  is  heated  to  such  a 
temperature  as  is  necessary  to  create  a  sufficient  motive 
column  in  the  shaft  for  the  proper  ventilation  of  the  mine, 
but  the  flame  of  the  furnace  cannot  reach  the  point  in  the 
shaft  where  the  return  current  laden  with  explosive  gases 
enters.  This  point  is  at  least  50  yards  above  the  bottom  of 
the  shaft,  depending  on  the  size  of  the  furnace,  the  depth 
of  the  shaft,  and  the  gaseous  character  of  the  mine. 

39.  Pressure  Due  to  a  Furnace. — The  unit  of  venti- 
lating pressure  in  furnace  ventilation  is  equal  to  the  differ- 
ence between  the  weight  of  a  column  of  air  heated  to  a 
certain  temperature  by  a  furnace  and  the  weight  of  an  air 
column  of  equal  height  but  not  artifically  heated.  This 
second  air  column  may  be  an  air  column  in  the  outside 
atmosphere,  as  cd,  Fig.  12,  having  a  height  corresponding  to 
the  depth  of  the  furnace  shaft,  or  it  may  be  an  air  column  in 
the  downcast  shaft  or  slope  ac,  Fig.  11,  or  it  may  be  com- 
posed of  both  an  inside  and  an  outside  column  E  C,  Fig.  14. 
This  latter  case  would  at  times  necessitate  considering  three 
temperatures;  namely,  that  of  the  outside  air  column  D  E, 
that  of  the  downcast  slope  or  shaft  column  CD,  and  that  of 
the  upcast  or  furnace  shaft  column  A  B. 

It  is  evident  from  the  explanation  given  under  Natural 
Ventilation  that  the  unit  pressure  any  furnace  can  produce 
will  depend  on  the  difference  in  the  weights  of  these  two  air 
columns.  To  determine  this  unit  pressure,  the  first  step  is 
to  calculate  the  weight  of  1  cubic  foot  of  air  having  a 
temperature  equal  to  the  average  temperature  of  the  down- 
cast air  column,  and  of  1  cubic  foot  of  air  of  the  same 
temperature  as  the  average  temperature  of  the  upcast 
column,  then  multiply  each  of  these  unit  weights  by  the 
heights  of  their  respective  air  columns,  and  the  difference 
between  the  weights  of  the  downcast  and  upcast  columns 
will  give  the  unit  of  ventilating  pressure.  Multiplying 
this  pressure  by  the  sectional  area  of  the  airway  gives  the 
total  pressure  producing  circulation,  or  the  ventilating 
pressure  pa. 


54  MINE  VENTILATION  §14 

40.  Power  of  a  Mine  Furnace. — In  furnace  ventila- 
tion, as  in  natural  ventilation,  for  any  given  motive  column, 
which  determines  the  unit  of  ventilating  pressure,  the  velocity 
of  the  air-current  is  determined  by  the  rubbing  surface  and 
area  of  the  mine  airways.  As  explained  under  Natural 
Ventilation,  any  increase  in  the  rubbing  surface  of  the  mine 
or  airway  in  furnace  ventilation  causes  a  decrease  in  the 
power  on  the  air,  and  vice  versa,  any  decrease  in  the  rubbing 
surface  causes  an  increase  in  the  power  on  the  air  for  a  con- 
stant area.  This  means  that  the  same  depth  of  furnace  shaft 
and  the  same  conditions  with  respect  to  the  densities  of  the 
upcast  and  downcast  columns  will  develop  a  greater  or  less 
power,  according  as  the  rubbing  surface  of  the  mine  is  less 
or  greater  for  a  constant  area.  The  reason  for  this  is  that 
the  power  in  any  circulation  is  determined  by  the  quantity  of 
air  passing  in  the  airway  and  the  unit  of  ventilating  pressure 
causing  the  circulation;  that  is,  u  =  qp.  For  the  same  con- 
ditions of  the  furnace,  depth  of  furnace  shaft  and  densities 
of  upcast  and  downcast  columns,  the  unit  of  ventilating  pres- 
sure is  constant  and  the  quantity  of  air  in  circulation  varies 
inversely  as  the  rubbing  surface  for  a  constant  area. 

The  power  of  a  mine  furnace  may  be  found  from  the 
formula  for  horsepower  by  substituting  for  q  its  value  in 

the  formula  q  = 

. 

33,000    33,000     33,000 

EXAMPLE. — (a)  Find  the  unit  of  ventilating  pressure  produced  by 
a  mine  furnace  when  the  temperature  of  the  downcast  is  60°  and  that 
of  the  upcast  340°,  the  depth  of  the  furnace  shaft  being  1,500  feet. 
(b)  Find  the  quantity  of  air  in  circulation  in  this  mine,  the  size  of  the 
upcast  and  downcast  shafts  being  each  8  ft.  X  15  ft.  and  1,500  feet 
deep,  the  air  traveling  in  a  single  current  through  the  mine,  the  size 
of  the  airways  being  8  ft.  X  10  ft.  and  5,000  feet  long,  including  the 
return,  (c)  Find  the  horsepower  producing  the  circulation  in  this  case. 

SOLUTION. — (a)  Finding  the  motive  column  in  this  case,  in  terms 
of  the  downcast  air,  by  substituting  the  given  values  in  formula  1  of 
Art.  27, 


§  14  MINE  VENTILATION  55 

M  -  i  snn  34°  ~  6°  _  i  500  v  28°  =.  -M*  ft 
*  ~  1>500460T340       1>5°°  X  800 

The  weight  of  1  cu.  ft.  of  the  downcast  air  having  a  temperature  of 
60°  and  assuming  a  barometric  pressure  of  30  in.,  is 

1.3273  X  30       39.819 
w  =     460  +  60     "  -520T  =  -0766  lb"  nearfy 

The  unit  of  ventilating  pressure  is  then  found  by  multiplying  the 
motive  column  by  the  weight  of  1  cu.  ft.  of  the  downcast  air  which 
gives  p  =  525  X  .0766  =  40.2  lb.  per  sq.  ft.  Ans. 

(b)  It  will  be  necessary  here  to  calculate  the  rubbing  surface,  sec- 
tional area,  and  the  relative  potential  X  =  a\T~  =  \~  for  the  shafts 
and  the  mine  airways  separately;  thus, 

Two  shafts          f  *  =  2  X  1)500  X  2(8  +  15)  =  138'000  Sq'  ft' 
S    '    ' 


8  X  15  =  120  sq.  ft. 
Airways  (intake  Is,  =  5,000  X  2(8  +  10)  =  180,000  sq.  ft. 

and  return)   .  \a,  =  8  X  10  =  80  sq.  ft. 
The   general   expression   for   the   total    pressure   in   this   case,    as 

explained  in  Art.  13,  is  given  by  the  formula  p  =  k  Q"  (-pi  + 
Calculating  the  values  of  Xt  and  X*  for  the  shafts  and  airways, 

Xl  =  V— ,  or  XS  =  — ;  hence, 
1          s,        138,000         138,000          23 

Shafts>  x*  =  sf-  =  -y^  =  i^ooo  =  288  =  -0798'  nearfy 

Airways,  ^i  =  ^  =  ^  =  ^  =  ^=  3™.  nearly 

'l    +    *         ^ 

•**!  -^2 

Substituting  in  the  formula  given  the  values  for  p  and  -y-  +  -~-  and 

solving,  with  respect  to  0,  for  the  quantity  of  air  a  furnace  can  circu- 
late in  this  mine, 

40.2  =  .00000002  X  Q3  X  .4313  =  .000000008626  Q\ 

40  2     ~  

.000000008626  =^,660,329,237  =  68,300  cu.  ft.  per 

min.    Ans. 

(c)     The  power  on  the  air  in  this  circulation  or  the  power  of  the 
furnace  in  this  case  is  then, 

68,300  X  40.2 


,000  ~         33,000 

41.  Temperature  of  the  Air  in  Furnace  Ventila- 
tion.— Aside  from  the  effect  produced  on  the  density  of 
the  upcast  column  by  the  presence  of  mine  gases  in  the 


56  MINE  VENTILATION  §14 

upcast  air,  the  densities  of  both  the  upcast  and  downcast 
columns  are  determined  by  their  average  temperatures.  The 
average  temperature  of  the  downcast  column  will  seldom 
vary  to  any  extent  from  that  of  the  outside  air.  The 
average  temperature  of  the  upcast  or  furnace  column  is 
usually  estimated  as  equal  to  one-half  the  sum  of  the 
temperatures  at  the  bottom  and  at  the  top  of  the  furnace 
shaft,  respectively. 

Theoretically,  the  temperature  of  the  air-current  passing 
over  a  mine  furnace  is  determined  by  the  weight  and  heating 
value  of  the  coal  burned  per  hour,  and  the  weight  and 
specific  heat  of  the  air  passing  over  the  furnace  in  the  same 
period  of  time.  There  is,  however,  a  practical  limit  to  the 
rise  of  temperature  that  can  be  imparted  to  the  air  in  its 
passage  over  the  furnace,  owing  to  the  increased  velocity  of 
the  air-current  as  its  temperature  rises  and  the  depth  of  the 
furnace  shaft  increases.  Owing  to  the  greater  cooling  sur- 
face of  deep  shafts  and  the  generally  higher  velocity  of  the 
upcast  current,  the  average  temperature  of  the  column  of  air 
above  a  furnace  will  generally  be  lower  for  a  deep  shaft  than 
for  a  shallow  one;  this,  however,  is  not  an  absolute  rule,  as 
much  depends  on  the  quantity  of  coal  burned  per  hour  and 
the  mine  resistance,  which  determines  the  quantity  of  air  in 
circulation  for  any  given  air  column. 

The  unit  of  ventilating  pressure  that  a  mine  furnace  can 
produce  may  be  expressed  by  the  formula, 


EXAMPLE.  —  .(a)  Calculate  the  approximate  pressure  that  a  furnace 
can  produce  under  average  conditions,  at  a  depth  of  300  feet  below 
the  surface,  (b)  Find  the  approximate  pressure  due  to  a  furnace  at  a 
depth  of  600  feet. 

SOLUTION.—  (a)  Substituting  in  the  formula,  the  approximate  pres- 
sure at  a  depth  of  300  ft.  is 


=  -£=  =  10.59  Ib.  per  sq.  ft.     Ans. 


§14  MINE  VENTILATION  57 

(d)     Substituting  the  given  values  in  the  same  formula,  the  pressure 
due  to  a  furnace  at  a  depth  of  600  feet  below  the  surface  is 

p  =  -^2=  -  -|=  -  18.44  Ib.  per  sq.  ft.    Ans. 


42.  Coal  Burned  Per  Hour. — Under  the  ordinary  con- 
ditions in  furnace  ventilation  a  rise  of  temperature  varying 
from  300°  F.  to  500°  F.  is  produced  in  the  air  passing  over 
the  furnace.  The  weight  of  coal  necessary  to  be  burned  per 
hour  to  produce  the  required  rise  of  temperature  in  the  air- 
current  will  depend  on  the  heating  value  of  the  coal  and  the 
weight  and  specific  heat  of  the  air  to  be  heated  in  that  time. 
The  weight  of  air  in  circulation  multiplied  by  its  specific  heat 
will  give  the  total  heat  required  each  minute  to  produce  a  rise 
of  1°  in  the  temperature  of  the  air-current.  The  heat  required 
per  hour  to  raise  the  temperature  /  degrees  F.  is  then 
expressed  by  the  formula, 

A  =  Wt(Qw4>)  (1) 

in  which    J  =  total  heat  required,  in  British  thermal  units 

per  hour; 
/  =  the  rise  in  temperature  of  the  air  current  in 

degrees  F. 
Q  =  quantity    of   air  in  circulation,  in  cubic  feet 

per  minute; 
w  =  weight   of    air   before    reaching    furnace,    in 

pounds  per  cubic  foot; 
0  =  specific  heat  of  air-current,  in  British  thermal 

units. 

The  total  heat  required  as  given  by  the  formula  divided  by 
the  heating  value  of  the  coal  will  give  the  weight  of  coal 
required  in  pounds  per  hour. 

Assuming  an  average  value  of  12,000  British  thermal 
units  for  the  heating  value  of  the  coal,  and  an  average  rise 
of  temperature  demanded  of  the  furnace  of  400°  F.,  and 
ignoring  the  effect  of  moisture  and  gases  present  in  the 
upcast  current,  which  would  alter  to  some  extent  the  specific 
heat  of  the  upcast  air,  the  weight  of  coal  required  in  an 


58  MINE  VENTILATION  §14 

average  mine  furnace  is  given  approximately  by  the  follow- 
ing formula: 

C=36£«  (2) 

in  which    C  —  weight  of  coal  burned,  in  pounds  per  hour; 

Qm  =  number  of  thousands  of  cubic  feet  of  air  in 

circulation  per  minute. 

That  is  to  say,  under  ordinary  conditions  a  mine  furnace  will 
require  36  pounds  of  coal  per  hour  for  each  1,000  cubic  feet 
of  air  in  circulation.  The  following  examples  will  serve  to 
show  the  use  of  formulas  1  and  2: 

EXAMPLE  1.  —  Find  the  weight  of  coal  necessary  to  be  burned  per 
hour  to  produce  a  rise  of  temperature  of  400°  F.  in  an  air-current  of 
100,000  cubic  feet  of  air  per  minute,  assuming  the  weight  of  the  air 
before  reaching  the  furnace  is  .0766  pound  per  cubic  foot,  and  the 
specific  heat  of  the  air  .2374,  the  heating  value  of  the  coal  being  13,000 
British  thermal  units  per  pound. 

SOLUTION.—  Substituting  the  given  values  in  formula  1  and  dividing 
by  the  heating  value  of  this  coal,  letting  C  equal  the  required  weight 
of  coal, 

60  X400(100,0,X,X.  0766  X.  2374)  _ 


EXAMPLE  2.  —  What  weight  of  coal  will  be  required  per  hour  under 
ordinary  average  conditions  to  produce  a  circulation  of  40,000  cubic 
feet  of  air  per  minute? 

SOLUTION.—  Substituting  the  given  value  for  Qm  in  formula  2,  the 
required  weight  of  coal  in  this  case  is 

C  =  36  X  40  =  1,440  Ib.  per  hr.     Ans. 

43.  Area  of  Fire-Grate  Surface.  —  When  the  quantity 
of  air  is  known  or  has  been  determined,  as  previously 
explained,  the  weight  of  coal  that  must  be  burned  per  hour 
to  cause  a  rise  in  temperature  in  the  air-current  of,  say, 
400°  F.  is  first  found  by  formula  1  of  Art.  42.  The  area  of 
fire-grate  surface  required  to  burn  this  weight  of  coal  per 
hour  will  depend  chiefly  on  the  character  of  the  coal  and  is 
obtained  by  dividing  the  weight  of  coal  burned  per  hour  by 
the  amount  of  coal  consumed  per  hour  on  each  square  foot 
of  grate  surface  of  an  ordinary  furnace  when  the  draft  is 
about  the  same  as  that  produced  by  the  shaft  above  a 
mine  furnace.  Approximately,  for  rough  calculation,  15  to 


§14  MINE  VENTILATION  59 

25  pounds  of   coal  may  be  assumed  as  being  burned  per 
hour  on  each  square  foot  of  grate  surface. 

44.     The  fire-grate  surface  required  may  also  be  found 
by  the  following  formula  for  each  horsepower  of  the  furnace: 


in  which  D  =  depth  of  furnace  shaft,  in  feet; 

*  34  =  a  constant  number  proved  by  many  experi- 

ments; 

^  =  square  feet  of  fire-grate  surface  required  per 
horsepower  of  the  ventilation. 

EXAMPLE  1.  —  The  depth  of  the  shaft  is  400  feet,  and  the  horse- 
power required  in  the  ventilation  is  37.8;  what  area  of  fire-grate  is 
required? 

34 

SOLUTION.  —  By  applying  the  formula,  s  =  —  =  =  1.7  sq.  ft.  of  fire- 

A/400 

grate  surface  required  per  horsepower.     Since  37.8  H.  P.  is  required, 
the  fire-grate  surface  should  be  37.8  X  1.7  =  64.26  sq.  ft.     Ans. 

If  the  bars  of  the  fire-grate  are  5  feet  long,  the  breadth 

of  the  furnace,  in  feet,  will  in  this  case  be  equal  to  —  '-  — 

5 

=  12.85  feet. 

EXAMPLE  2.—  Let  a  furnace  shaft  be  900  feet  deep,  and  the  ventila- 
ting current  be  equal  to  200,000  cubic  feet  per  minute,  with  a  mine 
resistance  equal  to  2  inches  of  water  gauge;  what  must  be  the  breadth 
of  the  furnace  when  the  length  of  the  fire-bars  is  taken  at  5  feet? 

SOLUTION.  —  The   horsepower  required   is   found    by  the  formula 


_.  hence,  t  =        .  _  „,  H  p 

face  per  horsepower,  by  use  of  formula  for  grate  area  is  found  to  equal 

34 
—==  =  1.133  sq.  ft.;  and,  therefore,  the  square  feet  of  fire-grate  sur- 

face required  are  equal  to  63  X  1.133  =  71.379  sq.  ft.;  and,  if  the 
length  of  the  fire-bars  be  taken  at  5  ft.,  the  breadth  of  the  furnace  is 
equal  to  71.379  -=-  5  =  14.28  ft.  Ans. 

An  examination  of  the  two  examples  will  show  that,  not- 
withstanding the  fact  that  the  horsepower  required  in  the 
latter  case  is  so  much  greater  than  in  the  former,  yet  the 

145—19 


60  MINE  VENTILATION  §14 

grate   area  is  very  little  increased,   owing  to    the    greater 
depth  of  the   shaft. 

45.  Effect  of  Furnace  Stack.  —  It  is  customary  to 
erect  a  rough  board  stack  above  the  mouth  of  a  furnace 
shaft;  this  stack  is  not  usually  over  20  feet  in  height,  as  its 
main  object  is  to  protect  the  mouth  of  the  shaft  and  prevent 
persons  or  animals  from  falling  into  the  shaft,  but  at  the 
same  time  the  smoke  of  the  furnace  is  carried  above  the 
surface  and  a  better  draft  is  thereby  afforded.  Sometimes  a 
substantial  stack  of  considerable  height  is  erected.  In  any 
case,  the  erection  of  a  stack  over  the  furnace  shaft  has  the 
effect  of  increasing  the  depth  of  the  shaft  and  the  height  of 
the  furnace  column.  For  the  same  average  temperature  of 
the  furnace  shaft,  the  motive  column  and  the  pressure  are 
increased  in  the  ratio  of  the  height  of  this  column,  and  the 
quantity  is  increased  as  the  square  root  of  this  ratio. 

Calling  the  depth  of  the  shaft  D  and  the  height  of  the 
furnace  stack  S,  the  ratio  between  the  quantity  of  air  Q^  in 
circulation  without  the  stack  and  the  increased  quantity  of 
air  after  the  erection  of  the  stack  Q,  is 


^ 

Q*       V     D 

Hence,  for  the  increased  quantity  of  air  due  to  the  erection 
of  a  furnace  stack, 


EXAMPLE.  —  The  circulation  due  to  a  furnace  in  a  certain  mine  is 
20,000  cubic  feet  of  air  per  minute;  how  much  will  this  circulation  be 
increased  by  the  erection  of  a  stack  21  feet  high,  the  depth  of  the  fur- 
nace shaft  being  100  feet? 

SOLUTION.  —  The  increased  circulation  after  the  erection  of  the  stack 
in  this  case  will  be 

=  20,000  X  H  =  22,000  cu.  ft.  per  min. 

The  increase  due  to  the  stack  is,  therefore,  22,000  -  20,000  =  2,000 
cu.  ft.  Ans. 


§  14  MINE  VENTILATION  61 


EXAMPLES    FOB    PRACTICE 

1.  What  grate  surface  will  be  required  to  produce  a  current  of 
75,000  cubic   feet  per   minute,   assuming   a  fuel    consumption   of  25 
pounds  of  coal  per  hour  per  square  foot  of  grate?  Ans.  108  sq.  ft. 

2.  What  width  of  furnace  will  be  required  to  produce  a  current  of 
40,000  cubic  feet  per  minute,  taking  the  fuel  consumption  as  20  pounds 
of  coal  per  hour  per  square  foot  of  grate;  the  grate  bars  of  the  furnace 
are  6  feet  long?  Ans.  12  ft. 


MINE  VENTILATION 

(PART  3) 
MECHANICAL  VENTILATION 


INTRODUCTION 

1.  The  subject  of   mechanical  ventilation  embraces 
all  systems  of  ventilation  in  which  the  circulation  of  air  is 
produced  by  means  of  some  mechanical  device.     Some  of  the 
primitive  and  now  almost  obsolete  mechanical  methods  of 
producing  ventilation,  as  the  waterfall  and  the  wind  cowl,  are 
so  simple  that  they  are   often   included  under  the  head  of 
natural  ventilation. 

2.  Waterfall,  or  Trompe. — The  falling  of  water  down  a 
properly  arranged  vertical   shaft  is  capable  of  producing  a 
considerable  current  of  air  in  the  mine  below.     The  adoption 
of  this  means  of  ventilation,  however,  depends  on  an  abundant 
water  supply  and  natural  conditions  of  mine  drainage  such  as 
are  afforded  by  a  drainage  tunnel,  or  other  means  of  readily 
and  cheaply  disposing  of  the  water  at  the  foot  of  the  shaft. 
Without  these  features,  the  waterfall  cannot  be  permanently 
adopted,  but  it  may  be  used  for  producing  temporary  ventila- 
tion in  case  of  emergency.     On  account  of  the  burning  of  a 
large  breaker  and  the  destruction  of  the  ventilating  fans  at 
the  Pancoast  Colliery,  near  Scranton,  Pennsylvania,  the  expe- 
dient was  successfully  adopted  of  turning  a  stream  of  water 

Copyrighted  by  International  Textbook  Company.    Entered  at  Stationers'  Hall,  London 

§15 


MINE  VENTILATION 


§15 


down  one  of  the  shafts  for  the  purpose  of  temporarily  driving 
back  the  mine  gases  so  as  to  afford  protection  for  the  men 
while  fighting  the  fire  at  the  bottom  of  the  main  shaft,  beneath 
the  burning  breaker.  When  sinking  a  shaft,  a  small  amount 
of  water  may  be  poured  down  the  shaft  to  clear  away  the 
smoke  after  a  blast. 

The  trompe  shown  in  Fig.  1  is  still  used  in  some  metal- 
mining  districts  and  consists  of  a  vertical  space,  or  compart- 
ment, in  the  shaft,  in  which  inclined  shelves  a  are  arranged, 


FIG.  1 

over  which  the  water  pours  from  a  trough  or  ditch  b.  A  per- 
forated plate  c  is  placed  at  the  top  to  break  up  the  solid 
stream  of  water  into  numerous  small  streams  better  calculated 
to  entrap  the  air  in  falling  down  the  shaft.  Openings  d  are 
arranged  in  the  sides  of  the  compartment  for  the  admission 
of  air,  which  is  carried  down  the  shaft  by  the  falling  water. 
The  water  drops  into  a  basin  or  sump  at  the  bottom  of  the 
shaft,  while  the  air  is  thrown  out  into  an  air  drift  leading  to 
the  mine  airways. 


§15  MINE  VENTILATION  3 

3.  Instead  of  the  trompe  just  described,  a  brush  mat  is 
sometimes  arranged  at  the  top  of  the  shaft  to  receive  the 
stream  of  water,  which  filters  through  it  and  is  broken  into 
numerous  small  streams  of  water  that  drip  down  the  shaft. 
This  method  is  not  used  to  any  extent  at  the  present  time 
and   is    only   suggestive  of   means  that  might  be  adopted 
temporarily   or  in    an    emergency   that    has    destroyed    the 
ventilators  at  a  mine. 

4.  The  wind  cowl  is  any  contrivance  in  the  form  of  a 
sail  or  other  means  of  deflecting  the  natural  surface  winds 
into  the  mine  airways  so  as  to  produce  a  circulation  of  air 
through  the  mine.     The  arrangement  is  very  primitive  and 
can  be  used  only  as  a  temporary  means  of  ventilation  in  case 
of  emergency  or  for  the  sinking  of  a  shaft  or  for  the  venti- 
lation of  a  very  small  mine. 

5.  The  steam  jet,  or  blower,  is  an  appliance  used  for 
producing  a  draft  or  current  by  the  force  of  steam  escaping 
from  a  pipe  or  nozzle;  it'  gives  good  results  in  creating  a 
comparatively  small  current  of  air  as,  for  instance,  under  a 
boiler,   but   the    application   to   mine   ventilation  is   limited 
to  the  ventilation  of  a  shaft  or  slope  during  sinking  or  to 
a  small  shaft  or  slope  mine. 


VENTILATING  FANS 

6.  Classification. — A  ventilating  fan  is  a  device  for 
producing  a  current  of  air  by  the  rotation  of  flat  or  curved 
blades  or  paddles  attached  by  arms  to  a  central  shaft  called 
the  fan  shaft.  Mine  ventilating  fans  are  divided  into  two 
general  classes,  depending  on  the  principle  of  their  action. 
These  two  classes  are  disk,  or  propeller,  fans  and  centrifugal 
fans.  A  large  number  of  fans  of  different  makes  and  styles 
belonging  to  each  of  these  two  classes  are  now  in  operation 
and  giving  good  satisfaction  as  mine  ventilators.  Centrif- 
ugal fans  are,  however,  by  far  the  more  numerous,  particu- 
larly for  mine  ventilators  and  for  supplying  large  volumes 
of  air. 


MINE  VENTILATION 


§15 


DISK    FANS 

7.  The  distinguishing  features  of  a  disk,  or  propeller, 
fan,  Fig.  2,  are  the  shape  and  position  of  the  blades  a, 
which  resemble  the  arms  of  an  anemometer,  or  the  blades 
of  a  propeller.  The  blades  are  attached  to  a  central  hub  b 
on  the  shaft  c.  This  shaft  is  revolved  by  a  crank  or  a  belt 
operated  by  an  engine  or  by  an  electric  motor  d,  as  shown. 
On  account  of  the  high  speed  at  which  electric  motors 


FIG.  2 

usually  run,  it  is  necessary  to  use  the  gears  e  and  /  to  give  a 
suitable  speed  for  the  fan.  The  blades  are  supported  from 
the  center  by  the  stay-rods  g  and  are  connected  by  the  short 
rods  h.  The  casing  i  acts  mainly  as  a  protection  for  the 
blades.  In  a  windmill  or  anemometer,  the  force  of  the  wind 
acting  on  the  wheel  causes  it  to  revolve,  but  in  the  disk  fan 
the  revolution  of  the  wheel  by  the  fan  motor  moves  the  air 
and  produces  a  current  in  the  airway. 

The  disk  fan  has  the  following  advantages  and  disadvan- 
tages:    It  is  easily  erected,  and  the  first  cost  of  the  fan  and 


§15  MINE  VENTILATION  5 

of  its  erection  is  small.  The  air-current  may  be  reversed  by 
simply  reversing  the  direction  of  the  revolution  of  the  fan. 
It  can  be  run  at  a  high  speed  by  a  motor  directly  connected 
with  the  fan  shaft.  The  great  disadvantage  of  the  disk  fan 
is  that  it  is  not  possible  with  it  to  give  a  large  volume  of 
air  at  a  high  water  gauge,  or,  in  other  words,  when  there 
is  considerable  mine  resistance.  Beyond  a  certain  volume  of 
air  delivered  by  the  fan  at  a  low  water  gauge,  its  capacity  is 
limited,  and  the  volume  cannot  be  largely  increased  by 
increasing  the  speed  of  the  fan  as  is  possible  with  fans  of 
the  centrifugal  type.  

CENTRIFUGAL    FANS 

8.  General  Definitions. — Fig.  3  shows  the  general 
arrangement  of  the  simplest  form  of  the  centrifugal  fan,  the 
fan  wheel  or  the  revolving  portion  only  being  shown  with- 
out any  casing  or  support  for  the  wheel.  The  blades  a  are 
straight  and  radial  and  are  made  up  of  flat  plates  of  metal 
or  wood.  In  large  fans  these  are  often  joined  together  by 
the  broad,  thin  metal  plates  b,  or  by  nar- 
row metal  rings.  In  small  fans,  there  is 
often  no  connection  between  the  blades. 

Two  fan  circles  are  shown;  the  inner 
circle  ccc  is  the  circumference  of  the 
intake  opening  and  is  sometimes  called 
the  intake  circle;  the  outer  circle  ddd  is 
the  circumference  of  the  fan.  The  diam- 
eter of  the  fan,  sometimes  also  called  the 
outer  diameter,  is  the  diameter  of  the 
outer  circle;  the  inner  diameter  of  the  fan 
is  the  diameter  of  the  inner,  or  intake, 
circle.  Likewise,  the  outer  and  inner  radii  of  the  fan  are  the 
radii  of  the  outer  and  inner  circles,  respectively.  The  depth, 
or,  as  it  is  sometimes  called,  the  length,  of  the  fan  blades,  is 
the  difference  between  the  outer  and  inner  radii  or  the  radial 
distance  ef  between  the  two  fan  circles. 

The  width  of   a  blade  eg  is  the  width  of  the  fan.      The 
outside  line  eg  is  the  tip  of  the  blade  and  the  inside  line  / h 


6  MINE  VENTILATION  §15 

is  the  lip  of  the  blade.  The  throat  of  the  fan  is  the  cylin- 
drical surface  described  by  the  lip  of  the  blade  or  the  line  f  h 
when  the  fan  is  revolved. 

Commonly,  the  outer  diameter  and  the  width  are  the  dis- 
tinguishing dimensions  of  a  centrifugal  fan,  but  the  diameter 
of  the  intake  circle  should  also  be  mentioned,  or  the  depth  of 
the  blade.  The  description  of  a  fan  should  also  state,  besides 
the  number  of  blades,  their  position  with  respect  to  a  radial 
line  arid  whether  they  are  straight  or  curved,  and  if  curved 
give  an  outline  of  the  curvature. 

Centrifugal  fans  may  be  divided  into  two  general  classes — 
open-running  fans  and  closed-running  fans — differing  in  the 
manner  in  which  the  air  is  discharged  from  the  fan.  Open- 
running  fans  have  no  casing  surrounding  the  circumference 
of  the  fan,  the  air  being  discharged  from  the  fan  at  once 
into  the  atmosphere,  all  around  the  circumference.  In 
closed-running  fans,  the  air  is  discharged  from  the  fan, 
at  'its  circumference,  into  an  enclosed  air  space  or  passage 
that  surrounds  the  circumference  of  the  fan,  often  called 
the  spiral  passage  or  spiral  conduit^  by  which  it  is  conducted 
either  into  the  fan  drift  leading  to  the  mine,  or  into  a  chim- 
ney opening  to  the  atmosphere. 

Centrifugal  fans  also  differ  essentially  from  each  other  in 
the  following  points:  the  shape  and  number  of  the  blades; 
the  curvature  of  the  blades;  the  position  of  the  blades  with 
respect  to  a  radial  line;  the  expansion  of  the  spiral  casing 
surrounding  closed-running  fans;  the  expansion  of  the  chim- 
ney; the  style  of  cut-off;  and  the  general  proportions  of  the 
fan.  Each  of  these  features  contributes  its  share  to  increase 
or  decrease  the  general  efficiency  of  the  fan  as  a  ventilating 
motor  and  will  be  treated  separately. 

9.     Principle  of  Action  of  the  Centrifugal  Pan. — The 

principle  on  which  a  centrifugal  fan  acts  is  as  follows: 
The  air  contained  between  the  fan  blades  has  a  certain 
weight  and  when  the  fan  is  revolved  a  certain  force  is  devel- 
oped, called  a  centrihigal  force,  that  acts  on  each  particle  of 
the  air  in  revolution  and  tends  to  throw  it  outwards  or  away 


§15  MINE  VENTILATION  7 

from  the  fan  shaft  and  toward  the  circumference.  The  air 
within  the  fan  being  free  to  move  in  a  radial  direction,  when 
acted  on  by  this  force,  moves  outwards,  or  toward  the  cir- 
cumference of  the  fan.  This  movement  of  the  air  outwards 
in  a  radial  direction  causes  an  area  of  depression,  or  partial 
vacuum,  within  the  fan,  and  the  outside  air  under  the  influ- 
ence of  the  atmospheric  pressure  at  once  flows  into  this 
area  of  depression.  The  air  enters  the  fan  at  the  center  and 
flgws  toward  the  circumference,  where  it  is  discharged.  This 
action  is  continuous  and  causes  an  uninterrupted  flow  of  air 
into  and  through  the  fan  as  long  as  the  fan  is  revolved.  A 
centrifugal  fan  thus  produces  motion,  or  velocity,  in  the  air 
within  and  surrounding  the  fan.  If  resistance  to  the  flow  of 
the  air  is  present  at  the  intake  opening  of  the  fan,  a  depres- 
sion or  fall  of  pressure  below  the  atmospheric  pressure  is 
caused  at  that  point;  but  if  the  resistance  is  present  at  the 
discharge  opening  of  the  fan,  a  compression  of  the  air  is 
caused  at  that  point,  and  a  pressure  above  the  atmospheric 
pressure  results.  Therefore,  in  the  ventilation  of  a  mine  or 
airway,  the  fan  will  create  a  pressure  below  the  atmospheric 
pressure  when  the  intake  of  the  fan  is  connected  with  the 
mine  or  airway,  but  when  the  discharge  opening  of  the  fan 
is  connected  with  the  mine  or  airway  a  pressure  above 
the  atmospheric  pressure  is  produced.  In  the  former  case, 
the  fan  is  called  an  exhaust  fan;  in  the  latter  case,  a  force 
fan,  blower  fan,  or  blow-down  fan. 


DETAILS    OF    CONSTRUCTION 

10.  Support  of  Fan  Blades. — The  stability  of  a  fan 
depends  largely  on  the  manner  of  connecting  the  fan  wheel 
with  the  central  shaft  by  which  it  is  rotated.  A  common 
form  of  support  consists  of  two  cast-iron  rings  z,  Fig.  3, 
called  spiders,  that  vary  in  diameter  according  to  the  size 
of  the  fan.  These  spiders  are  fitted  closely  to  the  fan 
shaft  o,  to  which  they  are  keyed  at  a  distance  apart  corre- 
sponding to  about  the  width  of  the  fan.  The  radial  arms  /, 
to  which  the  fan  blades  are  attached,  are  firmly  bolted  to 


8 


MINE  VENTILATION 


§15 


these  spiders.  While  this  construction  gives  a  firm  support 
to  the  blades,  the  spiders  and  radial  arms  in  this  position 
offer  an  unnecessary  obstruction  to  the  air  entering  the  fan, 


FIG.  4 

and  they  reduce  the  intake  area.  A  better  form  of  construc- 
tion, and  one  that  has  been  largely  adopted  since  its  intro- 
duction, is  shown  in  Figs.  4 
and  5.  The  method  of  sup- 
porting the  blades  there  shown 
provides  an  unobstructed  open- 
ing into  the  fan,  giving  a  greater 
efficiency  at  less  cost.  Instead 
of  the  two  spiders  set  apart,  one 
on  each  side  of  the  fan  as  in 
Fig.  3,  two  conical  castings  a, 
Fig.  4,  are  set  back  to  back  at 
the  center  of  the  fan  shaft  oo, 
to  which  they  are  keyed.  The 
radial  arms  b  are  of  boiler-plate 
steel,  and  are  broadened  at  the 
base  where  they  fit  into  and  are 
FlG'5  firmly  bolted  between  the  two 

castings  a,  a.  In  this  construction,  there  is  but  one  radial 
arm  for  each  blade  and  each  arm  is  firmly  riveted  to  the 
center  .of  a  blade  A  by  means  of  angle  irons  c .  The  sides 


§15  MINE  VENTILATION  9 

of  the  blades  are  supported  either  by  an  annular  ring  of 
steel  plate  d  whose  width  is  equal  to  the  depth  of  the  fan 
blades,  as  shown  in  Fig.  4,  or  by  means  of  two  narrow 
rings  a,  a,  Fig.  5,  set  into  the  blade  so  as  to  be  flush  with 
the  side  edge.  The  construction  shown  in  Fig.  4  would 
also  be  used  in  an  open-running  fan,  the  sides  of  the  fan 
wheel  in  this  case  taking  the  place  of  the  fan  casing.  In  a 
closed-running  fan,  however,  this  would  be  a  waste  of 
material.  Angle  irons  e  are  used  to  stiffen  the  sides  of  the 
blades,  in  either  case,  and  to  the  inner  ends  of  these  angle 
irons  one  end  of  the  sway-braces  /  is  riveted.  The  other  end 
of  the  braces  /is  bolted  to  the  central  casting  a  and  by  means 
of  these  braces  the  whole  system  of  blade's  is  tied  together 
and  stiffened  so  as  to  prevent  any  side  motion  or  swaying  of 
the  blades.  Instead  of  a  plain  ring  at  the  lip  of  the  blade, 
-an  angle  iron  b,  Fig.  5,  is  sometimes  used,  one  arm  of  which 
projects  beyond  the  edge  of  the  fan  casing  so  as  to  form  a 
collar  that  fits  into  the  intake  opening.  This  completely 
closes  the  space  at  each  side  of  the  fan  at  this  point  and 
overcomes  the  tendency  of  the  air  to  escape  and  cause 
eddies.  In  order  that  the  air  may  enter  into  the  intake 
opening  regularly  and  evenly  from  all  directions,  a  con- 
choidal  ring  is  sometimes  used  as  shown  at  c,  Fig.  5,  the 
depth  of  this  ring  varying  from  12  to  18  inches,  according 
to  the  size  of  the  fan. 

11.  The  Fan  Casing  or  Housing. — Except  in  open- 
running  fans  that  discharge  their  air  into  the  atmosphere 
all  around  the  circumference,  it  is  necessary  to  encase  the 
entire  fan  so  as  to  conduct  the  air  discharged  from  the  fan 
into  the  fan  drift  or  by  a  special  passage  into  an  expanding 
chimney  from  which  it  escapes  into  the  atmosphere.  The 
casing  surrounding  the  fan  is  called  the  fan  housing. 
An  open-running  fan  only  requires  a  sufficient  housing  to 
carry  the  air  from  the  fan  drift  leading  from  the  mine  to 
each  side  of  the  center  of  the  fan. 

In  a  closed-running  fan,  the  fan  wheel  is  enclosed  in  a 
special  casing  or  housing.  The  fan  casing  consists  of  two 


10 


MINE  VENTILATION 


§15 


flat  sides  with  central  openings  corresponding  to  the  intake 
openings  of  the  fan,  the  outer  line  of  the  casing  taking  the 
form  of  the  spiral  so  as  to  provide  a  gradually  expanding 
air  passage  surrounding  the  circumference  of  the  fan. 
Fig.  6  gives  the  general  outline  of  the  fan  wheel  and  the 
spiral  casing,  together  with  the  expanding  chimney  into 
which  the  fan  discharges  its  air  when  exhausting.  The 
center  of  the  fan  wheel  is  at  o\  a  a  is  the  inner  and  b  b 
the  outer  fan  circle,  the  heavy  lines  a  b  being  the  fan  blades. 
The  outer  line  of  the  casing  of  the  fan,  starting  from  the 
points  where  it  is  tangent  to  the  inner  vertical  line  cd  of  the 
chimney,  follows  the  circumference  of  the  fan  wheel  as 
far  as  the  point  <?,  the  portion  ce  being  the  arc  of  a  circle 

having  a  length  equal 
to  at  least  the  distance 
between  two  consecu- 
tive blade  tips.  From 
the  point  e,  the  casing 
expands  uniformly, 
forming  the  spiral  efg 
around  the  circumfer- 

ence    of   the   fan,    and 

, 

becoming  tangent  to 

the  outer  line  ghol  the 

.  6  chimney  at  a  point  g. 

The  point  c  is  called  the  point  of  cut-off,  because  at  this  point 
the  air  passing  between  the  blades  of  the  fan  is  cut  off  from 
passing  up  the  chimney.  The  portion  of  the  fan  casing  ce 
being  the  arc  of  a  circle,  fits  closely  to  the  outer  fan  circle, 
and  there  is  but  about  1  inch  of  clearance  between  them. 
The  purpose  of  this  is  to  cut  off  any  connection  between  the 
spiral  space  surrounding  the  fan  and  the  chimney,  at  this 
point,  thus  compelling  all  the  air  entering  the  spiral  from 
the  fan  to  flow  around  the  fan  in  the  direction  in  which  the 
blades  revolve.  This  causes  a  uniform  flow  of  the  air 
around  the  fan  and  prevents  the  formation  of  eddies.  When 
the  casing  is  thus  parallel  to  the  periphery  of  the  wheel  for 
a  distance  ce,  there  is  no  air  passing  through  the  first 


§15 


MINE  VENTILATION 


11 


compartment  ce  of  the  fan,  as  this  is  for  a  moment  practically 
closed  by  the  casing. 

From  <?,  the  fan  casing  should  expand  uniformly  around  the 
fan  so  that  the  sectional  area  of  the  spiral  passage  will 
increase  uniformly  with  the  number  of  compartments  dis- 
charging into  it,  and  the  velocity  of  the  air  at  all  points  of 
the  casing  will  then  be  the  same.  The  velocity  of  the  air 
in  the  spiral  passage  at  the  point  of  cut-off  is,  therefore, 
equal  to  the  total  quantity  of  air  passing  through  the  fan 
divided  by  the  sectional  area  of  the  passage  at  that  point. 
The  sectional  area  at  the  point  of  cut-off  is  equal  to  the 
width  of  the  fan  multiplied  by  the  distance  eg  from  the  point 
of  cut-off  perpendicular  to  the  outer  side  of  the  spiral. 

12.  The  method  of  laying  out  the  fan  spiral  is  as  follows: 
For  a  blower  fan,  locate  the  center  T,  Fig.  7,  of  the  fan  with 
respect  to  the  shaft  or  fan  drift  through  which  the  air  is  to  be 
drawn  so  that  the  spiral  passage  of  the  fan  may  be  expanded 
easily  to  connect  with  the  line  of  this  shaft  or  drift.  With  an 
exhaust  fan,  the  spiral  is  not  connected  with  the  mine  opening 
and  is  not  therefore  de- 
pendent on  it.  Using  the 
point  so  taken  as  a  center, 
describe  the  inner  and 
outer  fan  circles  with  radii 
Ta  and  Tb,  Next,  select 
for  the  point  of  cut-off  c 
that  point  of  the  outer  fan 
circle  where  the  tangent 
to  the  circle  will  make  the 
best  connection  with  the  FIG- 7 

chimney  for  an  exhaust  fan  or  with  the  fan  drift  or  shaft 
curbing  for  a  blower  fan.  From  the  point  of  cut-off,  the 
fan  casing  follows  the  arc  of  a  circle  for  a  distance  at  least 
equal  to  the  distance  between  two  consecutive  blade  tips 
of  the  fan;  i.  e.,  from  c  to  e.  The  spiral  is  then  started  at 
this  point  e  of  the  circumference  of  the  fan  and  is  laid 
out  by  means  of  a  wire  or  string  s  wound  about  a  small 


12  MINE  VENTILATION  §15 

circular  wooden  templet  or  disk  T  securely  fixed  at  the 
center  of  the  fan  so  that  the  disk  or  templet  cannot  revolve. 
The  diameter  of  the  templet  must  be  such  that  the  unwinding 
of  the  string  as  the  spiral  is  described  will  produce  the 
required  expansion  at  the  point  of  cut-off.  If  the  spiral  is 
started  at  a  distance  from  the  point  of  cut-off  equal  to  one- 
fifth  of  the  circumference  of  the  fan,  the  diameter  of  the 
small  templet  should  be  about  three-eighths  of  the  expan- 
sion of  the  casing  at  the  end  of  the  spiral  g  nearly  opposite 
the  point  of  cut-off;  that  is,  in  Fig.  7,  ij  is  three-eighths 
of  fg.  The  diameter  of  the  templet  must  be  determined 
for  each  fan  by  trial.  Having  described  the  fan  circles 
and  the  spiral  as  far  as  the  point  g  opposite  the  point 
of  cut-off,  this  point  is  connected  by  an  easy  curve  or 
tangent  with  the  line  of  the  fan  drift  or  shaft  curbing  for  a 
blower  fan;  and  when  an  exhaust  fan  and  chimney  are  used, 
the  tangents  to  the  fan  circle  at  the  point  of  cut-off  and  to 
the  spiral  are  extended  to  form  the  sides  of  the  expanding 
chimney.  Sometimes,  the  expansion  of  the  chimney  is 
increased  by  starting  the  tangent  to  the  spiral  before  the 
point  of  cut-off  is  reached.  This  gives  a  wider  and  naturally 
a  shorter  chimney  than  where  the  tangent  is  started  at  a 
point  opposite  the  point  of  cut-off. 

13.  The  fan  chimney  is  a  simple  chimney  expanding  as 
shown  in  Fig.  6.  The  width  of  the  chimney  perpendicular  to 
the  plane  of  revolution  is  generally  constant  and  corresponds 
with  the  width  of  the  fan  casing,  the  expansion  being  produced 
in  a  direction  corresponding  to  the  plane  of  revolution  of  the 
fan.  This  chimney  is  sometimes  called  the  SvasS  chimney. 
The  purpose  of  the  expanding  chimney  is  to  reduce  the 
velocity  of  the  air  after  passing  through  the  fan,  so  that  it  is 
discharged  into  the  atmosphere  at  a  low  velocity.  The  inner 
wall  c  d  of  the  chimney,  which  is  tangent  to  the  circumfer- 
ence of  the1  fan  at  c,  is  preferably  made  vertical,  the  expan- 
sion being  produced  entirely  by  the  inclination  of  the  outer 
wall  gh.  When  the  inner  wall  of  the  chimney  is  inclined 
toward  the  fan  and  the  outer  wall  made  vertical,  there  is  a 


15 


MINE  VENTILATION 


13 


decided  tendency  of  the  air-current  to  strike  against  the  outer 
wall  and  be  deflected  to  such  an  extent  as  to  produce  eddies, 
thus  decreasing  the  efficiency  of  the  chimney.  The  lower  end 
of  the  chimney  is  sometimes  called  the  throat  of  the  chimney, 
but  must  not  be  confused  with  the  throat  of  the  fan. 

14.  Fan  Shutter. — The  shutter  of  a  fan  is  a  sliding  door 
or  shutter  a,  Fig.  8,  so  arranged  as  to  slide  up  and  down  the 
back  face  of  the  fan  chimney  and  by  means  of  it  the  point  of 
cut-off  may  be  shifted  farther  up  or  down  the  chimney, 
thereby  increasing  or  decreasing  the  area  for  the  discharge 
of  air  from  the  fan.  The  shutter  is  supported  by  the 


PIG.  8 

chains  e  attached  to  a  windlass  /  by  which  it  is  raised  and 
lowered.  The  purpose  of  the  shutter  is  to  reduce  the 
vibrations  set  up  in  the  fan  and  which  are  often  due  to  lack 
of  proper  proportionment  of  the  different  parts  of  the  fan. 
Another  cause  of  vibration  is  the  striking  of  the  air-current 
against  abrupt  angles  or  surfaces,  by  which  means  eddies  are 
established  in  the  current.  At  times,  the  cause  of  vibration 
in  the  fan  lies  wholly  outside  of  the  fan  itself,  these  vibrations 
being  transmitted  from  the  point  of  disturbance  through  the 
air  to  the  plates  of  the  fan,  which  are  sensitive  to  vibration. 
Vibration  is  often  caused  by  the  rapidly  succeeding  blows 


14 


MINE  VENTILATION 


§15 


produced  on  the  air  when  the  blade  tips  of  the  fan  pass  an 
abrupt  cut-off. 

Vibration  may  be  prevented  in  great  part  by  the  use  of  the 
Y-shaped  cut-off,  as  shown  by  the  lower  edge  bed  of  the 
shutter  in  Fig.  8,  so  that  the  air  is  cut  off  gradually  instead 
of  instantly  when  the  fan  blades  pass  this  point.  The  apex 
of  the  Y  should  be  at  the  center  c  of  the  cut-off  plate  or 
shutter,  and  the  Y  should  point  in  the  direction  in  which  the 
fan  revolves.  What  is  called  the  Walker  shutter  is  a  mov- 
able plate,  or  shutter,  having  the  cut-off  edge  of  the  shutter 
in  the  shape  of  a  Y,  as  shown  in  the  figure.  The  use  of  the 
shutter  for  the  purpose  of  stopping  vibration  in  a  fan  is  fast 
becoming  obsolete,  owing  to  the  greater  care  taken  in  fan 
design,  and  because  the  use  of  a  shutter  may  decrease  the 
discharge  of  the  fan. 

15.  Fan  Pit  and  Foundation. — In  order  to  reduce  the 
height  of  the  fan  above  the  surface  of  the  ground  and  tc 
increase  its  stability,  a  part  of  the  wheel  revolves  in  a  pit  a, 
Fig.  9,  called  the  Ian  pit.  This  pit  is  walled  in  with  brick 


FIG.  9 

as  shown  in  Fig.  9,  or  with  concrete,  as  shown  in  Fig.  10, 
and  these  walls  also  generally  form  the  foundation  for  the  fan- 
shaft  journals  c  and  the  fan  casing.  The  depth  of  the  pit  is  such 
that  the  lowest  point  b,  Fig.  9,  of  the  intake  circle  is  about  level 
with  the  ground.  From  4  to  6  inches  of  rock  ballast  is  often 


§15 


MINE  VENTILATION 


15 


first  laid  in  the  bottom  of  the  excavation  for  the  pit  and 
leveled;  this  is  covered  with  a  bed  of  concrete  or  brick.  The 
floor  and  walls  of  this  pit,  when  it  is  completed,  form  a  sec- 
tion of  the  lower  portion  of  the  fan  casing,  and  must  be  made 
smooth  and  flush  with  the  fan  casing  built  over  this  founda- 
tion. The  foundation  walls  may  be  carried  above  the  ground 
as  high  as  the  center  of  the  fan,  and  the  journals  or  bearings 


Showing  connection  wffft  Snafr,  Blow- Jown  fan 

(a) 
FIG. 10 

for  the  fan  shaft  can  then  be  set  directly  on  a  solid  foundation, 
or  the  journals  may  rest  on  pedestals  as  illustrated  in  Fig.  9. 
Anchor  bolts  e  are  built  into  the  foundation  walls  to  hold 
the  journal-boxes  in  place. 

The  fan  shaft  o  must  be  of  sufficient  length  to  afford  good 
bearings  on  each  side  of  the  fan  and  with  large  fans  these 


16  MINE  VENTILATION  §15 

bearings  are  often  water-jacketed  to  prevent  the  overheating 
of  the  journals.  When  the  fan  is  built  to  exhaust,  in  order 
that  the  engine  d  may  not  be  too  close  to  the  fan  intake  and 
thus  interfere  with  the  entry  of  air  into  the  fan,  three  journals 
are  required,  one  on  each  side  of  the  fan  pit  and  one  outside 
of  the  fan  drift  next  to  the  engine.  Every  precaution  must 
be  taken  to  prevent  the  settlement  of  the  foundation  on 
which  the  journals  rest,  as  a  slight  settlement  of  one  of  the 
bearings  may  break  a  fan  shaft  or  result  in  other  serious 
injury  to  the  fan. 

16.     Connection  of  Fan  With  Mine  Opening. — The 

position  of  the  fan  with  respect  to  the  mine  opening  and  its 
connection  with  the  opening  depend  on  the  kind  of  mine 
opening,  on  the  type  of  fan,  and  on  the  local  arrangements 
about  the  opening.  The  fan  should,  of  course,  be  placed  so 
that  it  will  not  interfere  with  the  arrangements  for  hoisting 
and  hauling.  The  intake  opening  of  a  mine  should  be 
located  so  that  air  entering  the  mine  may  be  as  pure  and 
free  from  dust  as  practicable. 

Fig.  10  shows  an  arrangement  for  a  blower  fan  connected  to 
a  mine  shaft  a;  (a)  is  the  elevation,  and  (£)  the  plan.  A  sim- 
ilar arrangement  could  also  be  adapted  to  a  drift  opening. 
The  foundation  c  for  the  fan  in  this  case  is  of  concrete  and 
the  lower  part  of  the  foundation  is  shown  stepped  to  save 
material.  The  foundations  are  represented  as  carried  up 
only  to  the  ground  line,  and  this  necessitates  supporting  the 
journals  of  the  fan  shaft  o  on  heavy  iron  pedestals  d  with 
broad  bases  securely  bolted  to  the  foundation  walls.  The 
steel  housing  of  the  fan  is  also  set  on  this  foundation  and 
firmly  bolted  by  means  of  anchor  bolts.  The  engine  house  6 
joins  the  fan  casing  at  the  corner,  and  an  opening  /  is  left  in 
the  end  of  the  engine  house  for  the  passage  of  the  connecting- 
rod  of  the  engine.  This  is  necessary  in  order  not  to 
obstruct  the  intake  opening  on  this  side  of  the  fan,  and  to 
enable  the  air  to  be  drawn  from  the  outside  atmosphere  into 
the  fan  through  both  of  the  intake  openings.  As  shown  in 
the  plan,  the  fan  is  direct-connected  to  the  engine  g.  The 


§15 


MINE  VENTILATION 


17 


center  of  the  fan  is  set  back  a  short  distance  only  from  the 
side  of  the  shaft  a  and  in  line  with  the  center  of  the  shaft. 

Fig.  11  shows  an  exterior  of  a  blower  fan  and  engine 
house  similar  to  that  shown  in  Fig.  10,  but  seen  from  the 
other  side.  The  casing  or  fan  house  #,  is  made  of  boiler 
plate  steel  strengthened  by  angle  irons  b. 

The  arrangement  illustrated  in  Figs.  10  and  11  is  not  well 
adapted  to  a  gaseous  mine,  as  the  air-current  cannot  be 
quickly  reversed  when  such  a  change  is  required. 

17.  Reversing  the  Air-Current. — It  is  always  advis- 
able to  arrange  the  ventilator  of  a  large  mine,  and  especially 


FIG.  11 


a  gaseous  one,  so  that  the  air-current  can  be  reversed 
promptly  in  case  of  emergency.  In  the  mine,  the  reversal  of 
the  current  will  of  course  tend  to  open  all  the  doors  to  a 
greater  or  less  extent,  depending  on  the  force  of  the  current, 
and  this  will  prevent  a  very  large  proportion  of  the  air  from 
circulating  through  the  mine.  It  is,  however,  often  neces- 
sary to  produce  this  change  in  the  direction  of  the  air-current 
in  order  to  permit  rescue  parties  to  enter  the  mine  in  case  of 
accident,  and  to  drive  back  the  gases  that  would  otherwise 
be  forced  into  the  workings  and  suffocate  or  otherwise 


18  MINE  VENTILATION  §15 

endanger  the  workmen  before  they  could  make  their  escape. 
The  ventilation  of  every  large  and  gaseous  mine  should  be 
carefully  arranged  with  respect  to  such  an  emergency,  and 
escape  ways  provided  and  kept  open  by  which  the  men  can 
be  got  out  of  the  mine. 

The  action  of  the  fan  is  the  same  before  and  after  reversing 
the  current.  The  air  still  enters  the  fan  at  the  center  and  is 
discharged  at  the  circumference.  When  the  fan  is  blowing 
or  forcing  air  into  the  mine,  the  intake  openings  of  the  fan 
must  be  open  to  the  atmosphere  and  the  discharge  of  the 
fan  must  then  be  connected  with  the  fan  drift  or  shaft  lead- 
ing to  the  mine.  Doors  are  provided,  however,  by  "which 
this  order  may  be  reversed  so  that  the  intake  openings  of 
the  fan  may  be  connected  with  the  fan  drift  or  shaft  leading 
from  the  mine,  while  the  discharge  is  then  closed  to  the 
mine  and  opened  to  the  atmosphere.  This  changes  the  fan 
from  a  blowing,  or  forcing,  fan  into  an  exhaust  fan.  Such 
an  arrangement  is  shown  by  Fig.  12. 

In  the  arrangement  shown  in  Fig.  12,  the  center  of  the 
fan  is  set  some  distance  back  from  the  shaft  so  as  to  afford 
room  for  the  doors  a  b  and  de  used  in  reversing  the  air-cur- 
rent. The  section  of  the  fan  shown  does  not  give  the  struc- 
tural details,  but  is  merely  diagrammatic.  The  center  line 
of  the  fan  is  placed  on  line  with  the  center  of  the  shaft. 
Two  side  drifts  /  are  provided,  connecting  the  intake  open- 
ing at  each  side  of  the  fan  with  the  main  fan  drift  g,  at 
a  short  distance  from  the  side  of  the  shaft.  At  the  junction 
of  the  main  and  side  air  drifts,  shunting  doors  are  arranged 
as  shown  in  the  plan,  Fig.  12  (a).  These  doors  are  for  the 
purpose  of  connecting  the  side  drifts -with  the  atmosphere  or 
with  the  main  drift  leading  to  the  shaft  and  the  mine,  as  may 
be  desired.  The  full  lines  a  b  and  de  show  the  position  of 
the  doors  when  the  side  drifts  and  intake  openings  of  the 
fan  are  connected  with  the  main  drift,  and  the  fan  is  running 
as  an  exhaust.  The  dotted  lines  ac  and  db  show  the  position 
of  these  doors  when  the  side  drifts  and  intake  openings  are 
connected  with  the  atmosphere.  In  this  position  of  the 
doors,  the  main  drift  g  is  open  to  the  spiral  passage,  which 


20  MINE  VENTILATION  §15 

is  the  discharge  opening  of  the  fan  and  closed  to  the  intake 
openings,  and  the  fan  is  running  as  a  blower.  In  the  figure, 
the  arrows  show  the  direction  of  the  air-current  coming  from 
the  shaft  and  passing  through  the  side  drifts  into  the  intake 
openings  of  the  fan,  whence  it  passes  radially  through  the 
fan  and  is  conducted  by  the  spiral  passage  to  the  chimney, 
where  it  is  discharged  into  the  atmosphere.  By  this  arrange- 
ment, the  air  is  exhausted  from  the  mine  by  the  action  of 
the  fan. 

When  the  position  of  the  doors  is  changed  to  that  indicated 
by  the  dotted  lines  ac  and  db,  the  air  from  the  outside 
atmosphere  will  enter  the  intake  openings  of  the  fan,  and 
after  passing  through  the  fan  will  be  conducted  by  the  spiral 
passage  to  the  main  drift  g  and  thence  forced  into  the  mine. 
In  order  to  deflect  the  air  passing  through  the  spiral  passage 
and  cause  it  to  enter  the  main  drift  and  shaft  instead  of 
passing  out  through  the  chimney,  a  second  door  ij  is 
arranged  near  the  foot  of  the  chimney,  and  this  is  swung 
into  the  position  indicated  by  the  dotted  line  ik,  the  point  k 
being  the  point  of  cut-off  where  the  outer  fan  casing 
starts.  By  means  of  this  door,  the  spiral  passage  of  the 
fan  may  be  connected  either  with  the  chimney  or  with  the 
main  drift  g. 

18.  Explosion  doors  should  be  provided  in  the  fan 
drift  as  shown  at  h.  These  doors  are  so  heavy  that  they 
cannot  be  opened  by  the  ordinary  pressure  of  the  air  in  the 
fan  drift,  but  in  case  of  an  explosion  they  will  be  blown 
open  and  the  greater  part  of  the  pressure  of  the  explosion  thus 
taken  off  the  fan. 

To  prevent  accidents,  it  is  provided  by  law  in  many  states 
that  the  ventilating  fan  must  be  run  continuously  night  and 
day  unless  the  mine  suspends  operations  indefinitely.  It 
cannot  be  stopped  or  the  direction  of  the  current  reversed 
without  the  permission  of  the  superintendent  or  manager  of 
the  mine  and  due  notice  of  any  stopping  of  the  fan  must  be 
posted  conspicuously  at  the  mine  opening  giving  the  hours 
when  the  fan  will  be  stopped. 


§15  MINE  VENTILATION  21 

TYPES    OF    CENTRIFUGAL,    FANS 

19.  The   most   prominent  types  of   fans  in  use  at  the 
present  time  are  the  Nasmyth^  Guibal,  Waddle,  Schiele^  and 
Capell.      These   types  embody  practically   all  the   essential 
features  of  fan  construction,  but  there  are  numerous  modifi- 
cations and  combinations  of  the  general  types.     Numbers 
of  fans,  such  as  the  Combes,  Biram,  and   Rittinger,  have 
been   designed  embodying    features-  that   have   since   been 
proved  to  be  valueless.     The  failure  of  most  of  these  types 
of  fans  was  due  to  features  that  reduced  the  strength  of  the 
centrifugal    force   developed   in   the   fan,   as,   for  example, 
improper   curvature    of   the    fan   blades,   or   the    too    great 
expansion  of  the  fan  casing,  while  in  many  cases  the  con- 
struction of  the  fans  was  too  complicated  and  expensive  to 
render  them  serviceable  for  mine  work.      Only  such  types 
of  fans   will  be  here  described  as  are  in  common  use  and 
which  will  illustrate  the  leading  features  of  centrifugal  fans. 

20.  Nasmyth  Fan. — The   general  arrangement  of  the 
Nasmyth  fan  -wheel  has  been  shown  in  Fig.  3.     This  fan 
is  probably  the  earliest  type  of  centrifugal  fan  as  it  is  the 
simplest.     It  is  open-running  and  discharges  its  air  into  the 
atmosphere  all  around  the  circumference.    No  provision  is 
made  to  reduce  the  shock  given  to  the  entering  air  by  the 
revolving  blades,  or  to  reduce  the  tendency  of  the  air  to 
produce  eddies  in  passing  through  the  fan.     The  blades  are 
straight   and   radial    and    are    supported    on   a   number   of 
radial  arms  that  are  firmly  attached  to  central  spiders  or  iron 
castings  z,  fitted  to  the  fan  shaft.     Some  fans  of  this  type 
are  in  use  at  the  present  time,  the  advantage  claimed  for 
them  being  the  simplicity  of  their  construction,  reduction  of 
first  cost  and  a  fair  amount  of  efficiency  when  operated  under 
low  water  gauges. 

21.  Gulbal  Fan. — The  first  of  the  early  types  of  cen- 
trifugal fans   that  marked    a   decided   improvement  in  fan 
construction   and  efficiency  was   the   Guibal.     One   of  the 
characteristic  features  of  this  fan  is  the  construction  of  the 


22  MINE  VENTILATION  §15 

frame  that  supports  the  fan  blades.  This  frame  at  each  side 
of  the  fan  consists  of  a  series  of  bars  a,  Fig.  13,  bolted  to  a 
spider  b  on  the  fan  shaft  and  also  bolted  together  so  that  the 
outer  end  of  each  bar  forms  a  support  for  the  blade,  while 
the  inner  end  of  the  bar  serves  as  a  brace  to  strengthen 
another  blade.  This  construction  is  cheap  and  effective 
in  furnishing  a  substantial  fan  wheel,  but  the  supporting 
bars,  on  account  of  their  size  and  number,  and  the  central 
spiders  obstruct  the  flow  of  air  through  the  fan  and  thus 
decrease  its  efficiency.  The  Guibal  fan  is  encased  in  a 
housing  that  forms  a  circle  that  fits  closely  to  the  outer 
circle  of  the  fan  wheel  for  about  three-fourths  of  the  circum- 
ference of  the  fan.  At  this  point,  the  expansion  of  the  casing 
begins  and  is  made  sufficiently  rapid  to  connect  with  the 
outer  line  of  the  chimney.  The 
Guibal  chimney  is  compara- 
tively tall  and  narrow,  and  at 
its  lower  end  is  supplied  with 
a  movable  or  sliding  shutter, 
so  that  the  sectional  area  at 
the  throat  of  the  chimney  can 
be  decreased  or  increased  as 
Pm.  13  desired. 

The  disadvantage  of  the  close-fitting  casing  in  the  original 
Guibal  fan  was  soon  manifested  when  the  work  of  this  fan 
was  compared  with  that  of  other  types.  As  a  result,  there 
are  at  the  present  time  improved  Guibal  fans  erected  in 
which  the  expansion  of  the  casing  has  been  carried  farther 
around  the  circumference  of  the  fan  so  as  to  increase  the 
spiral  air  passage.  This  has  given  an  added  efficiency  to  the 
Guibal  fan  and  the  improved  fan  with  spiral  casing  is  capable 
of  giving  a  good  quantity  of  air  against  a  fairly  high  water 
gauge  or  mine  resistance. 

It  is  important  to  note  that  the  blades  of  the  Guibal  fan 
are  straight  but  not  radial;  in  the  general  type  of  this  fan, 
they  are  inclined  at  an  angle  of  about  45°  with  a  radius  pass- 
ing through  the  inner  edge  or  lip  of  the  blade.  This  posi- 
tion of  the  blade  allows  the  entering  air  to  slide  on  to  the 


§15 


MINE  VENTILATION 


23 


blade  with  less  shock  than  in  the  straight  radial  blades  of  fans 
of  the  Nastnyth  type,  but  when  the  blades  are  not  radial  the 
centrifugal  force  by  means  of  which  the  air  is  thrown  out 
from  the  fan  is  greatly  reduced. 

22.     Waddle  Fan. — The  general  form  of  the  Waddle 

fan  is  shown  in  Fig.  14.     The  blades  are  curved  backwards 


FIG.  14 

from  the  direction  of  motion  and  are  so  tapered  toward  the 
circumference  as  to  maintain  a  unform  sectional  area  for  the 
passage  of  the  air  through  the  fan.  The  fan  is  open-running 
and  there  is  no  casing  surrounding  it,  but  the  air  is  discharged 
at  once  into  the  atmosphere  all  around  the  circumference  of 
the  fan.  In  order  to  protect  the  discharge  opening  at  the 
circumference  of  the  fan  and  to  reduce  to  some  extent  the 


24 


MINE  VENTILATION 


§15 


velocity  of  the  air  discharged  into  the  atmosphere,  the  sides 
of  the  more  recent  forms  of  this  fan  have  been  extended 
beyond  the  blades  at  the  circumference  so  as  to  form  an 
expanding  flange  on  each  side  of  the  opening. 

The  construction  of  the  Waddle  /an  is  complicated  and 
expensive.  The  fan  is  designed  to  produce  a  fair  quantity 
of  air  against  a  high  water  gauge,  but  gives  in  general  a 
low  efficiency.  It  receives  its  air  on  one  side  only,  but  the 
air  is  guided  into  the  fan  by  inclined  passages  so  as  to 
reduce  the  shock  of  the  revolving  blades.  In  the  later 
forms  of  the  Waddle  fan,  the  intake  area  is  supplied  with 
inclined  wings  or  scoops  designed  to  assist  the  entry  of  air 
into  the  fan.  The  fan  is  commonly  built  with  a  large  diameter 
giving  a  "high  peripheral  speed  for  a  moderate  speed  of  the 
engine.  A  diameter  of  40  feet  is  not  uncommon  and  fans  of 
even  larger  diameter  have  been  used.  In  common  with  other 
open-running  fans,  there  is  an  almost  total  absence  of  vibra- 
tion in  the  Waddle  fan. 

23.  Schiele  Fan. — The  characteristic  features  of  the 
Schlele  fan,  Fig.  15,  are  a  spiral  casing,  curved  and 


FIG.  15 


tapered  blades,  and  a  central  disk  or  plate  that  practically 
divides  the  fan  at  the  center  into  two  single  intake  fans,  and 


§15 


MINE  VENTILATION 


25 


furnishes  the  necessary  support  for  the  fan  blades.  Like 
the  Waddle  fan,  the  blades  a  are  curved  backwards  from  the 
direction  of  motion  and  are  tapered  toward  the  circumference, 
as  shown  in  Fig.  19,  Art.  41,  so  as  to  produce  a  uniform 
section  of  area  for  the  passage  of  the  air  through  the  fan. 
Unlike  the  Waddle  fan,  however,  the  Schiele  fan  is  enclosed 
with  a  spiral  casing  b  that  expands  rapidly  around  the  circum- 
ference in  the  direction  in  which  the  fan  revolves. .  The 
effect  of  the  spiral  casing  is  almost  lost,  however,  because  of 
its  large  size.  The  fan  is  practically  an  open-running  fan  but 
enclosed  in  a  large  space  or  chamber  from  which  the  air  is 
discharged  through  an  expanding  chimney  into  the  atmos- 
phere. The  fan  is  practically  a  double  intake  fan  receiving 
its  air  from  both  sides,  but  into  separate  compartments,  how- 
ever. It  is  run  at  a  high  speed  and  gives  a  large  volume  of 
air,  under  a  low  water  gauge.  The  fan  is  usually  driven  by 
a  belt  and  pulley  in  order  to  obtain  the  high  speed  desired. 

24.  The  Capell  fan  is  one  of  the  more  recent  types  of 
centrifugal  ventilators,  and  its  general  arrangement  and 
characteristic  features  are  shown  in  Fig.  16.  It  has  two  sets 


PIG. 16 


of  wings,  one  set  a  extending  from  the  circumference  of  the 
intake  circle  to  the  perimeter  of  the  fan;  these  are  called  the 
outer  wings,  and  in  exhaust  fans  are  usually  made  to  fall  back 
on  a  simple  curve  away  from  the  direction  of  the  rotation; 


26  MINE  VENTILATION  §15 

in  a  blowing  fan,  they  are  usually  but  not  always  reversed. 
Another  set  of  wings  b,  called  the  inner  wings,  extend  from 
the  circumference  of  the  intake  toward  the  center  of  the  fan; 
these  wings  are  not  set  parallel  to  the  axis  of  the  fan  but  at 
an  angle  with  it,  which  angle  is  varied  with  the  conditions 
under  which  the  fan  operates.  The  wings  always,  however, 
lead  in  the  direction  of  rotation.  The  two  sets  of  wings  a 
and  b  are  solidly  joined  together  by  the  rings  c.  Curved 
vanes  d,  called  scoops,  are  placed  at  the  intake  with  their  lead- 
ing ends  bent  in  the  direction  of  rotation.  These  scoops  are 


"Pic.  17 

intended  to  gather  in  the  air  as  the  fan  revolves.  They  pro- 
ject a  few  inches  outside  the  body  of  the  fan  and  are  usually 
made  in  one  piece  with  the  inner  plates  b  and  are  riveted  to 
arms  e  made  of  angle  iron.  These  arms  are  bolted  to  a  cen- 
tral hub  and  to  the  rings  c.  In  the  center  of  the  breadth  of 
the  fan,  there  is  a  steel  disk  /,  which  is  connected  to  the  shaft 
by  means  of  hubs,  as  shown.  To  this  disk,  stays  g  are 
bolted,  the  other  end  of  each  stay  being  riveted  to  a  blade  a 
to  stay  it.  In  the  original  Capell  fan,  the  large  outer 
blades  a  were  curved  well  backwards  from  the  direction  of 
rotation  and  terminated  in  a  tangent  to  the  circumference  of 


§15  MINE  VENTILATION  27 

the  fan.  In  the  more  recent  forms  of  the  Capell  fan,  the 
shapes  of  the  outer  blades  have  been  materially  changed  so 
that  they  terminate  normally  to  the  circumference,  thus 
increasing  the  ability  of  the  fan  to  give  a  high  water  gauge. 
The  fan  is  usually  designed  to  run  at  a  high  speed  and  is 
much  smaller  in  diameter  than  the  fans  of  the  Guibal  type 
designed  to  give  an  equal  volume  of  air. 

25.     Robinson  Fan. — The   Robinson  fan,    shown   in 
Fig/  17,  consists  of  two  sets  of  curved  blades  a  divided  by  a 


FIG.  18 

central  disk  b  of  sheet  iron.  This  disk  is  bolted  to  a  cone  c 
in  the  center,  which  deflects  the  air  entering  the  fan  and  thus 
gradually  changes  its  direction.  The  rim  d  that  encircles  the 
cast-iron  spiders  e  revolves  just  inside  of  the  edges  of  the 
housings  /.  The  ends  of  the  blades  a  are  covered  by  plates  g 
that  revolve  just  inside  the  housing  h.  This  fan  is  designed 
to  give  a  large  quantity  of  air  at  a  high  water  gauge. 

26.     Sirocco  Fan. — The  Sirocco  fan,  Fig.  18,  represents 
a  recent  revival  of  some  of  the  early  ideas  in  regard  to 


28  MINE  VENTILATION  §15 

centrifugal  fans,  as  illustrated  by  the  Combes  and  the  Biram 
fans.  The  Sirocco  is  a  high-speed  fan  that  can  hardly  be 
described  as  a  mine  fan,  although  an  attempt  has  been  made 
to  introduce  it  in  mine  work.  This  fan  consists  of  a  large 
number  of  small  blades  a  attached  to  rings  b  that  are  sup- 
ported from  the  center  by  the  rods  c.  The  chief  objection 
to  this  small  high-speed  fan  is,  however,  the  limited  extent 
to  which  its  capacity  may  be  increased. 


FAN    DESIGN 

27.  General  Considerations. — The  ventilation  of 
every  mine  is  a  separate  problem;  and  in  order  to  secure 
the  best  results,  such  a  plan  of  ventilation  should  be  adopted 
in  the  mine  as  will  make  it  possible  to  maintain  a  mine 
resistance  within  certain  limits.  A  ventilator  should  then  be 
designed  and  constructed  to  suit  the  conditions  and  the  limits 
of  mine  resistance  adopted  for  the  given  mine.  To  make 
this  clear,  it  is  only  necessary  to  recall  the  fact  that  the 
mine  resistance  changes  rapidly  with  the  development  and 
extension  of  the  workings.  The  application  of  a  certain 
horsepower  against  a  given  mine  resistance  will  produce  a 
given  quantity  of  air  at  a  certain  water  gauge  or  pressure, 
but  the  development  of  the  mine  by  increasing  the  rubbing 
surface  increases  the  mine  resistance;  and  unless  it  is 
possible  to  increase  at  the  same  time  the  sectional  area  of 
the  airways  through  the  mine  by  splitting  the  air-current,  the 
quantity  of  air  furnished  by  a  given  power  will  decrease. 
It  is  often  possible  and  practicable  to  maintain  the  mine 
resistance  within  the  limits  of  the  power  of  the  ventilator, 
as  every  well-designed  ventilator  is  capable  of  a  considerable 
range  in  speed  without  a  great  loss  of  efficiency,  but  beyond 
these  prescribed  limits  a  decrease  or  increase  of  speed  is 
had  at  a  large  expense  of  efficiency.  When  this  point  is 
reached  in  the  requirements  at  the  mine,  it  should  be  possible 
to  make  some  change  in  the  circulation  of  the  air  through 
the  mine  so  as  to  again  reduce  the  mine  resistance  and 
perhaps  make  possible  a  slower  speed  of  the  fan.  In  certain 


§15  MINE  VENTILATION  29 

cases,  it  will  be  found  impracticable  or  impossible  to  do  this, 
while  in  other  instances  a  proper  system  or  plan  of  ventila- 
tion adopted  when  the  mine  is  first  opened  will  make  it 
possible  and  economical. 

In  designing  a  mine  fan  due  regard  should  be  had  for  the 
elevation  of  the  proposed  ventilator  above  sea  level  and  the 
average  atmospheric  conditions  of  temperature  and  moisture 
under  which  the  work  must  be  performed.  The  treatment 
of  the  subject  of  the  design  and  construction  of  mechanical 
ventilators  will  be  given  briefly  and  only  the  essential  points 
mentioned,  as  the  detailed  design  of  a  mine  fan  to  meet  all 
of  these  conditions  should  be  attempted  only  by  a  competent 
engineer  who  has  had  experience  in  the  work  of  designing 
ventilators.  The  treatment  of  the  subject  will  be  based  on 
experimental  data,  which  is  now  commonly  used  in  designing 
mine  fans. 

28.     Size    of     Intake    Opening,    Inner    Diameter. 

When  practicable,  the  fan  should  always  take  air  from  both 
sides,  the  prime  object  being  to  get  the  air  into  the  fan  with 
as  little  loss  of  power  as  possible.  For  a  given  atmospheric 
pressure  or  a  given  elevation  above  sea  level,  a  certain  centrif- 
ugal force  produces  a  certain  depression  or  vacuum  within 
the  fan  and  a  certain  velocity  of  the  air  entering  the  fan, 
depending  on  the  resistance  affecting  the  inflow  of  air  into 
the  fan. 

Experiment  has  shown  that  the  best  results  are  obtained 
when  the  velocity  of  the  air  entering  the  fan  is  estimated  at 
from  1,000  to  1,500  feet  per  minute,  1,200  feet  per  minute 
being  a  good  average  velocity.  This  velocity  forms  the 
basis  for  calculating  the  size  of  a  centrifugal  fan.  To  assume 
a  higher  velocity  of  the  entering  air  would  be  to  contract  the 
intake  opening  and  largely  increase  the  resistance  of  the  fan 
and  decrease  its  efficiency. 

The  quantity  of  air  Q  entering  the  fan  with  this  velocity, 
calling  the  inner  diameter  of  the  fan  d,  is  for  a  single 
intake,  Q  =  1,200  (.7854  </')  =  942.48  d*-,  for  a  double  intake, 
Q  =  1,200  X  2  (.7854  </')  =  1,884.96  rf1,  from  which  the 

145—21 


30  MINE  VENTILATION  §15 

diameter  of  the  intake  opening  is  obtained  by  the  following 
formulas: 

Single  intake,      d  =  .03257  V0  (1) 

Double  intake,    rf=.023V0  (2) 

Thus,  for  a  given  style  of  fan,  the  size  of  the  intake  opening 
or  the  inner  diameter  of  the  fan  depends  only  on  the  quantity 
of  air  in  circulation. 

EXAMPLE. — (a)  Find  the  diameter  of  the  central  orifice  of  a  single- 
intake  fan  designed  to  furnish  90,000  cubic  feet  of  air  per  minute. 
(b)  What  will  be  the  diameter  of  the  intake  of  a  fan  that  receives  its 
air  from  both  sides  for  the  same  quantity  of  air  in  circulation? 

SOLUTION.— (a)  Substituting  the  given  values  in  formula  1  for  a 
single-intake  fan, 

d  =  .03257  V90.000  =  9.771,  approximately,  9  ft.  9  in.    Ans. 
(b)     For  a  double-intake  fan  designed  to  furnish  the  same  quantity  of 
air  as  in  the  previous  case,  substituting  the  given  values  in  formula  2, 
d  =  .023V907XJ6  =  6.9,  say  7  ft.    Ans. 

29.  Breadth  of  Fan. — The  air  passing  through  the 
intake  circles  of  the  fan  is  deflected  through  an  angle  that  is 
approximately  a  right  angle  before  it  passes  into  the  space 
between  the  fan  blades.  This  change  in  the  direction  of  the 
current  causes  either  a  loss  of  velocity  or  an  absorption  of 
power.  If  the  velocity  of  the  air  passing  through  the  throat 
of  the  fan  were  the  same  as  the  entering  velocity,  the  area 
of  the  throat  would  be  equal  to  the  total  intake  area,  which 
for  double-intake  fans  is  the  sum  of  the  areas  of  the  two 
intake  circles.  It  may  be  assumed  that  the  loss  of  velocity 
due  to  the  deflection  of  the  current  does  not  exceed  20  per 
cent.,  which  makes  the  throat  velocity  of  the  air  eight-tenths 
of  the  entering  velocity.  To  allow  for  this  loss  of  velocity 
at  the  throat,  the  breadth  of  the  fan  should  be  such  that  the 
throat  area  will  be  increased  in  the  same  ratio  that  the 
velocity  is  decreased.  Or,  the  entire  intake  area  is  made  .8 
of  the  throat  area,  giving  the  formulas, 


Single  intake,         .8  b  (n  d}  =  (-  d*\ 
Double  intake     .8  6  (K  d)  =  2  (|  d*\ 


§15  MINE  VENTILATION  31 

Or,  for  the  breadth  of  the  fan, 
Single  intake,  b  =  •&  d         (1) 

Double  intake,         b  =  I  d          (2) 

EXAMPLE.  —  (a)  Find  the  diameter  of  the  intake  opening  and  the 
breadth  of  a  fan  designed  to  pass  40,000  cubic  feet  of  air  per  minute 
when  the  air  is  received  on  one  side  of  the  fan  only,  (b)  Find  the 
same  dimensions  of  a  double-intake  fan  designed  to  pass  the  same 
quantity  of  air. 

SOLUTION.  —  (a)  The  diameter  of  the  intake  opening  is  first  found 
by  substituting  the  given  values  in  formula  1  of  Art.  28.  Thus, 
d  =  .03257  V40.000  =  6.514,  about  6  ft.  6  in.  The  width  of  this  fan  is 
found  by  substituting  this  value  for  d  in  formula  1  of  this  article. 
Then, 

b  =  A  X  6.514  =  2.03,  about  2  ft.     Ans. 

(b)    For  a  double-intake  fan  passing  the  same  quantity  of  air,  the 
diameter  of  the  intake  opening  and  the  width  of  the  fan  are  as  follows: 
Inner  diameter, 

d  =  .023  V^  =  .023A/40.000  =  4.6,  about  4  ft.  7*  in.    Ans. 
Width  of  fan, 

=  2.875,  about  2  ft.  10i  in.    Ans. 


30.  Volume  of  Fan.  —  The  volume  of  a  fan  is  the  total 
air  space  between  the  fan  blades;  that  is,  it  is  the  space 
occupied  by  the  revolving  air.  The  volume  of  the  fan  and 
the  density  of  the  air  determine  the  weight  of  air  revolved 
by  the  fan,  and  the  amount  of  centrifugal  force  developed. 
Let  V  =  volume  of  fan,  in  cubic  feet; 

D  =  outer  diameter  of  fan,  in  feet; 
d  =  inner  diameter  of  fan,  in  feet; 
b  =  breadth  of  fan,  in  feet. 

Then,  for  fans  having  the  same  width  throughout, 
V=  .7854  (Da-d')t> 

EXAMPLE.  —  What  is  the  volume  of  a  fan  whose  outer  and  inner 
diameters  are  24  feet  and  12  feet,  respectively,  the  width  of  the  fan 
being  7  feet  6  inches? 

SOLUTION.  —  Substituting  the  given  values  in  the  formula, 
V  =  .7854(Z>*  -  d')t>  =  .7854(24'  -  12')7.5  =  2,544+  cu.  ft. 

Ans. 

If  the  weight  of  1  cubic  foot  of  this  air  is  .0788  pound,  the  weight 
of  air  revolved  in  the  fan  under  these  conditions  is  W  =  2,544  X  .0787 
=  200+  Ib. 


32  MINE  VENTILATION  §15 

31.  Centrifugal  Force  Developed  by  Revolution  of 
Fan. — If  a  fan  is  revolved,  a  force  is  set  up  that  tends  to 
throw  the  air  within  the  fan  radially  outwards;  this  force  is 
known  as  the  centrifugal  force.  It  may  be  calculated  by 
the  following  formula: 

F=™^  (1) 

gR* 

in  which  F  =  centrifugal  force,  in  pounds; 
W  =  weight  revolved,  in  pounds; 
vf  =  velocity  of  revolved  weight  W,  in  feet  per 

second; 

g  =  force  of  gravity,  expressed  in  feet  per  second; 
Re  =  distance    of   center   of    gravity   of   revolved 
weight  from  center  of  revolution,  in  feet. 
In  calculating  the  centrifugal  force  developed  by  a  fan,  the 
weight  of  air  in  each  compartment  of  the  fan  must  be  con- 
sidered.    In  calculating  the  centrifugal   force  produced  by 
the  revolution  of  the  fan,  the  weight  of  air  in  each  compart- 
ment is  assumed  to  be  concentrated  at  a  point  known  as  the 
center  of  gravity  of   the  air  in  the  compartment,  and  the 
velocity  of  revolution  vg  is  the  velocity  at  which  the  center 
of  gravity  revolves. 

The  distance  of  the  center  of  gravity  of  the  air  in  each 
compartment  Rg  from  the  center  of  the  fan  shaft,  assuming 
a  uniform  density  of  the  air  revolved  in  the  fan,  is  given 
by  the  formula, 


in  which    R  =  radius  of  outside  fan  circle,  in  feet; 
r  —  radius  of  inside  fan  circle,  in  feet. 

EXAMPLE. — What  centrifugal  force  is  developed  by  the  fan  in  the 
example  given  in  Art.  3O,  if  the  weight  of  air  revolved  is  200  pounds 
and  the  fan  makes  100  revolutions  per  minute? 

SOLUTION. — According  to  formula  2,  the  center  of  gravity  would  be 

\  (l2-  -  6')  =  I  ( w)  =  9<3+  ft-  fr°m  the  CeQter  °f  the  fa°  Sha£t- 
For  each  revolution  of  the  fan,  the  center  of  gravity  would  pass  over 
3.1416X18.6  =  58.43  ft.  If  the  fan  makes  100  rev.  per  min.,  the 


§15  MINE  VENTILATION  33 

velocity  of  the  center  of  gravity  would  be  5,843  ft.  per  min.,  or  approxi- 
mately 100  ft.  per  sec.    Then,  substituting  the  given  values  in  formula  1, 
„       Wv*        200  X  100'        fifi«71H      An 
F==  ^  =  32.16  X  9.3  =  6'6871b-     Ans' 

32.  Work  of  the  Centrifugal  Force. — If  a  force  acts 
on  a  body  free  to  move,  it  will  move  at  a  certain  velocity  and 
will  continue  to  move  at  this  velocity  unless  acted  on  by 
another  force,  which  increases  or  retards  the  original  velocity. 
If  the  force  continues  to  act  on  the  body,  the  velocity  will 
gradually  increase  and  the  rate  of  change  in  the  velocity 
is  called  the  acceleration. 

The  centrifugal  force  developed  by  the  revolution  of  a  fan 
is  continually  employed  in  imparting  velocity  to  a  given  mass 
of  air.  By  means  of  the  revolution  of  the  fan,  the  air  is 
brought  from  a  state  of  rest  outside  the  fan  to  a  state  of 
motion  within  the  fan  and  after  it  leaves  the  fan.  The 
power  applied  to  the  fan  shaft  is  not  entirely  converted  into 
power  on  the  air  in  the  airway,  but,  owing  to  frictional  and 
other  losses,  the  power  on  the  air  in  the  airway  is  not 
equal  to  the  power  applied  to  the  engine  or  other  motor 
that  moves  the  fan.  The  ratio  between  the  effective  power, 
that  is,  the  power  on  the  air  at  a  point  in  the  fan  drift  near 
the  fan,  and  the  power  applied  to  the  fan  shaft  expresses  the 
efficiency  of  the  fan.  If  F  represents  the  force  developed 
by  the  power  applied  to  the  fan  shaft,  and  K  the  efficiency 
of  the  fan,  the  power  on  the  air  at  or  near  the  fan  is  expressed 
by  K  F.  When  determining  the  efficiency  of  a  fan,  the  power 
on  the  air  should  be  measured  in  the  fan  drift  as  near  as 
practicable  to  the  fan  and  before  any  appreciable  amount  of 
the  power  has  been  used  in  overcoming  the  mine  resistance, 
but  at  a  sufficient  distance  from  the  fan  to  avoid  the  vari- 
ations in  pressure  and  velocity  in  the  fan  drift  just  at  the  fan; 
the  variations  are  greater  for  some  fans  than  for  others. 

In  explanation  of  the  mine  resistance  of  an  airway  in  Mine 
Ventilation,  Part  1,  it  was  shown  that  the  mine  resistance 
is  equal  to  the  total  ventilating  pressure  p  a  and  may 
be  represented  by  a  weight  W\  this  weight  W,  or  its 
equivalent  value  Pa,  divided  by  the  force  of  gravity  gives 


34  MINE  VENTILATION  §15 

the  expression  ^,  which  represents  the  mass  of  the  air  and 

g 

is  equivalent  to  the  mine  resistance  p  a  against  which  the  air 
is  accelerated  by  the  centrifugal  force  of  the  fan. 

A  force  producing  acceleration  in  a  body,  as  the  centrif- 
ugal force  of  the  fan  accelerates  a  given  weight  of  air,  is 
equal  to  the  mass  of  the  body  moved  multiplied  by  the 
acceleration  produced  in  feet  per  second;  or,  expressed  as 
a  formula, 

Fl  =  Af/=££/  (1) 

g 

in  which  Ft  =  force  moving  a  body,  in  pounds; 
M  =  mass  of  the  body  moved; 
/  =  acceleration  of  the  body,  in  feet  per  second; 
'P  =  unit  ventilating  pressure,  in  pounds  per  square 

foot; 

a  =  area  of  airway,  in  square  feet; 
g  =  acceleration  due  to  gravity,  32.16  feet  per 

second  at  sea  level. 
Then,  transposing  the  formulas, 


and,  since  Fl  =  KFt 

'-77*       (2) 

in  which,  in  addition  to  the  letters  just  given, 

F  =  centrifugal  force  developed  in  the  fan,  in  pounds: 
K  =  efficiency  of  fan 

EXAMPLE:.  —  Assuming  the  efficiency  K  of  the  fan  in  the  example  in 
Arts.  3O  and  31  to  be  60  per  cent,  and  the  water  gauge  against 
which  the  fan  is  operating  at  a  speed  of  100  revolutions  per  minute 
to  be  4  inches,  or  p  =  4  X  5.2  =  20.8  pounds  per  square  foot,  the 
sectional  area  a  of  the  fan  drjft  where  the  water  gauge  and  velocity 
of  the  air  is  measured  to  be  110  square  feet,  find  the  acceleration  due 
to  the  centrifugal  force,  which  was  found  to  be  6,687  pounds. 

SOLUTION.—  Substituting  the  values  given  in  the  formula, 


§15  MINE  VENTILATION  35 

The  foregoing  example  shows  that  the  centrifugal  force 
developed  in  this  fan  will  produce  against  the  resisting  con- 
ditions in  this  case  an  acceleration  of  56.4  feet  per  second. 
It  must  be  remembered,  however,  that  the  acceleration  is 
only  the  gain  in  velocity  per  second;  or,  starting  from  rest, 
it  is  the  velocity  attained  at  the  end  of  1  second  of  time. 
The  actual  velocity  developed  in  the  airway  will  depend  on 
the  length  of  time  during  which  acceleration  takes  place,  and 
this  depends  on  the  relation  between  the  power  and  the 
resistance.  The  total  power  U  of  the  ventilator  or  the 
work  performed  each  second  of  time,  however,  can  be  found 
by  multiplying  the  force  F  producing  motion  by  one-half  the 
acceleration  /  as  expressed  by  the  formula, 

U=F*^  (3) 

But  the  effective  work  or  the  power  on  the  air  Qp  for  a 
minute  of  time  is  60  (K ' U};  hence, 


=  60    A^  (4) 


33.  Quantity  of  Air  Delivered. — The  quantity  of  air 
that  this  fan  will  yield  under  the  given  conditions  is 
expressed  by  the  formula, 


Substituting  the  given  values  in  this  formula,  the  quantity 
of  air  is 

S=60/:604M87X544N 


20.8          '    2   / 
=  326,377,  say  330,000  cubic  feet  per  minute 

34.  Power  Required. — It  will  be  observed  from  the 
foregoing  that  the  volume  of  the  fan  determines  the  quan- 
tity of  air  the  fan  will  circulate  against  a  given  mine  resist- 
ance or  water  gauge.  The  power  required  to  turn  the  fan 
under  these  conditions  is  found  by  dividing  the  power  on  the 
air  Qp  by  the  efficiency  of  the  ventilator.  For  example,  the 
horsepower  required  to  operate  the  fan  in  the  example  in 


36  MINE  VENTILATION  §  15 

Art.  33  at  a  speed  of  100  revolutions  per  minute  under  the 
conditions  named  would  be 


It  may  be  explained,  briefly,  that  the  volume  of  the  fan 
determines  its  power.  But  the  volume  of  the  fan  depends 
on  the  two  dimensions,  the  width  of  the  fan  and  the  depth  of 
the  fan  blades,  and  these  dimensions  correspond,  respectively, 
to  the  quantity  of  air  in  circulation  and  the  unit  of  ventilating 
pressure.  In  general,  the  wider  the  fan  the  larger  is  the 
quantity  of  air  that  it  will  circulate  under  like  conditions; 
and  the  deeper  or  longer  the  fan  blades  the  greater  pressure 
will  the  fan  produce,  other  conditions  being  equal.  These 
remarks  are  suggestive  of  the  elements  of  design  of  centrif- 
ugal ventilators,  as  they  show  the  particular  effect  of  each 
dimension  of  the  fan. 

It  is  usually  assumed  that  the  quantity  of  air  furnished  by 
a  fan  is  proportional  to  the  speed  of  the  fan,  while  the  pres- 
sure of  the  air  is  proportional  to  the  square  root  of  the  speed. 

EXAMPLE  1.  —  If  a  tan  making  100  revolutions  per  minute  produces 
40,000  cubic  feet  of  air,  how  much  air  should  the  same  fan  produce 
in  the  same  airway  when  its  speed  is  increased  to  125  revolutions  per 
minute? 

SOLUTION.  —  Assuming  the  quantity  of  air  to  be  proportional  to  the 
number  of  revolutions  of  the  fan  per  minute,  the  quantity  produced 
by  the  fan  at  a  speed  of  125  revolutions  would  be 

^  X  40,000  =  50,000  cu.  ft.  per  min.    Ans. 

EXAMPLE  2.  —  If  a  fan  making  50  revolutions  per  minute  gives  a 
pressure  of  4.5  pounds  per  square  foot,  what  will  be  the  pressure  pro- 
duced in  the  same  airway,  if  the  speed  of  the  fan  is  increased  to 
75  revolutions  per  minute? 

SOLUTION.  —  Assuming  the  quantity  to  be  proportional  to  the  speed, 
since  the  pressure  varies  as  the  square  of  the  quantity,  the  pressure 
will  vary  as  the  square  of  the  speed,  or  50*  :  75"  =  4.5  :  x\ 

x  =  4.5  X  (jj\  "  =  10.12  Ib.     Ans. 

35.  Outer  Diameter  of  Fan.  —  In  a  well-designed  fan, 
the  outer  diameter  bears  a  certain  ratio  to  the  inner  diameter, 


§15  MINE  VENTILATION  37 

or  the  diameter  of  the  intake  opening,  which  is  an  element 
depending  alone  on  the  quantity  of  air  in  circulation.  A  for- 
mula expressing  the  ratio  of  the  outer  to  the  inner  diameter 
of  the  fan  is  as  follows: 


in  which    m  =  ratio  of  outer  to  inner  diameter  ( m  =  — ); 


Q  =  quantity  of  air  in  circulation,  in  cubic  feet 

per  minute; 
a  =  sectional  area  of  fan  drift  where  power  on  the 

air  is  measured,  in  square  feet; 
n  =  speed  of  rotation  of  fan,  in  revolutions  per 

minute; 
c  =  fan  constant,  ordinarily  c  —  4  to  6; 


The  value  of  the  fan  constant  will  vary  according  to  the 
style  of  the  fan  and  its  construction  with  respect  to  the 
amount  of  resistance  offered  to  the  passage  of  the  air 
through  the  fan,  but  in  general  this  value  may  be  assumed 
as  varying  from  c  =  4  to  c  =  1  .  The  more  obstructed  the 
intake  area,  or  the  greater  the  resistance  to  the  flow  of  air 
through  the  fan,  the  higher  will  be  the  value  of  this  constant. 
In  using  the  above  formula,  it  is  important  to  determine  by 
experiment  the  proper  constant  corresponding  to  the  condi- 
tions for  which  the  fan  is  designed.  This  formula  has  been 
developed  from  the  formulas  already  given,  and  an  example 
will  make  clear  its  use. 

EXAMPLE.—  Calculate  the  size  of  fan  required  to  deliver  200,000  cubic 
feet  of  air  per  minute  against  a  water  gauge  of  1.5  inches  at  a  speed 
of  60  revolutions  per  minute  under  normal  conditions. 

SOLUTION.  —  Assuming  a  double-intake  fan,  the  diameter  of  the 
intake  openings  of  this  fan  is  found  by  substituting  the  given  values 
in  the  formula, 

d  =  .023  V^  =  .023^200^00  =  10.28  ft.     Ans. 


38 


MINE  VENTILATION 


§15 


The  ratio  of  the  outer  diameter  to  the  inner  diameter  m  =     ,  is  then 

a 

determined  for  a  speed  of  rotation  n  =  60  revolutions  per  minute, 
assuming  a  sectional  area  of  the  fan  drift  a  =  120  square  feet,  by  sub- 
stituting the  given  values  in  the  formula  for  m;  thus, 


f  A/120  X  200,000 


/3,i 

f  \T7724, 
is  then  D 


+  1  =  2.387 

=  md  =  2.387  X  10.28 


The  outer  diameter  of   the  fan 
=  24.54  ft.    Ans. 

A  common  "rule  of  thumb"  makes  the  outer  diameter  of 
the  fan  twice  the  inner  diameter.  Although  this  rule  has 
been  widely  used,  it  does  not,  of  course,  consider  any  of  the 
conditions  that  should  properly  be  considered  in  the  design 
of  a  fan. 

36.  Expansion  of  Casing.  —  The  purpose  of  the  casing 
surrounding  the  fan  has  been  explained  in  the  general  descrip- 
tion of  centrifugal  fans.  The  amount  of  the  expansion  or  the 
maximum  depth  of  the  spiral  is  measured  at  the  point  of  cut- 
off. The  amount  of  this  expansion  at  the  cut-off,  assuming 
the  velocity  of  the  air  at  this  point  to  be  equal  to  the  speed  of 
the  fan-blade  tips  —  that  is,  the  peripheral  speed  —  is  calculated 
by  means  of  the  formula 

~  TiDnb 
in  which  e  =  expansion  of  casing  at  cut-off,  in  feet; 

Q  =  total  quantity  of  air  passing  in  cubic  feet  per 

minute; 

D  =  outer  diameter  of  fan,  in  feet; 
n  =  speed  of  rotation,  in  revolutions  per  minute; 
b  —  width  of  fan,  in  feet. 

EXAMPLE.—  Find  the  amount  of  expansion  of  the  outer  casing  of  a 
24-foot  fan  8  feet  wide,  designed  to  pass  200,000  cubic  feet  of  air  per 
minute  at  a  speed  of  60  revolutions  per  minute. 

SOLUTION.  —  Substituting  the  given  values  in  the  formula  the  expan- 
sion of  the  casing  is 


416  60X8 

37.     Number  of  Blades.  —  The  number  of  blades  in  a 
fan  is  important  in  order  that  the  air  shall  receive  sufficient 


§15  MINE  VENTILATION  39 

support  at  the  circumference  of  the  fan,  where  it  meets  the 
resistance  due  to  the  discharge  of  the  air-current  either  into 
the  atmosphere  or  into  the  spiral  conduit  surrounding  the  fan. 
The  number  of  the  fan  blades  should  be  proportional  to  the 
outer  circumference  or  the  diameter  of  the  fan,  and  inversely 
proportional  to  the  depth  of  tfte  fan  blades.  As  a  guide  in 
determining  the  number  of  blades  for  any  size  of  fan,  the 
following  formula  is  useful: 

D 


EXAMPLE;  1.  —  How  many  fan  blades  should  be  used  in  a  fan  10  feet 
in  diameter  when  the  depth  of  the  blades  is  2  feet? 

SOLUTION.  —  Subtracting  twice  the  depth  of  the  blades  from  the  outer 
diameter  of  the  fan  gives,  for  the  inner  diameter,  d  =  10  —  2  X  2  =  6  ft. 
Then,  substituting  values  in  the  formula  for  the  number  of  blades, 

N  =        D        =     ,  10       =  5  blades.    Ans. 
^D-d         VlO  -  6 

EXAMPLE  2.  —  How  many  blades  will  be  required  in  a  fan  32  feet  in 
diameter  and  having  an  intake  opening  16  feet  in  diameter? 

SOLUTION.  —  Substituting  the  given  values  in  the  formula  for  the 
number  of  blades, 

OO 


-, 

V32  -  16 


=  8  blades.     Ans. 


38.  Secondary   Blades.  —  It   is   often  a   good   plan  in 
building  a  large  fan  to  introduce  intermediate  or  supernumer- 
ary blades  or  wings  at  the  circumference  of  the  fan  midway 
between   the    regular   blades    to   prevent   the  formation  of 
eddies  toward  the  outer  edge  of  the  fan  wheel.     These  small 
blades  or  wings  should  conform  in  shape  and  position  to  the 
corresponding  portion  of  the  large  blades.     When  these  small 
blades  are  used,  the  number  of  large  blades  required  may  be 
taken  as  two-thirds  of  the  number  calculated  by  the  formula 
in  Art.  37. 

39.  Curvature  of  Blades.  —  Until  recently,  there  has 
been  a  wide  difference  of  opinion  in  regard  to  the  relative 
efficiency  of  straight  and  curved  blades.     The  straight,  or 
paddle,  blade,  as  it  is  often  called,  acts  only  to  revolve  the 


40  MINE  VENTILATION  §15 

air  passing  through  the  fan,  the  radial  velocity  being  imparted 
to  the  air  in  this  construction  wholly  through  the  agency  of 
the  centrifugal  force  developed  by  the  revolution.  The  incli- 
nation of  a  blade  backwards  from  the  direction  of  its  motion 
was  supposed  to  offer  a  less  resistance  to  the  passage  of  the 
air  through  the  fan.  It  was  f6rgotten,  however,  that  in  doing 
this  there  resulted  a  great  loss  in  the  centrifugal  force,  devel- 
oped, and  in  order  to  compensate  for  this  loss  it  was  neces- 
sary to  revolve  the  fan  at  a  much  higher  speed  when  the 
blade. s  were  curved  backwards  than  when  straight  blades 
were  used.  This  increase  of  speed,  in  most  cases,  is  accom- 
plished at  the  expense  of  efficiency. 

Recent  experiments  performed  in  England  and  in  this 
country  show  that  the  form  of  blade  giving  the  highest 
efficiency  is  that  in  which  the  blade  terminates  in  a  radial  line, 
or  the  end  of  the  blade  for  a  certain  distance  is  perpendic- 
ular to  a  tangent  to  the  circumference  at  that  point,  while  the 
lip  or  inner  edge  of  the  blade  is  curved  forwards  in  the  direc- 
tion of  motion  so  that  it  is  tangent  to  the  resultant  of  the 
velocity  of  the  entering  air  and  the  tangential  velocity  of 
the  lip  of  the  blade  at  the  throat  of  the  fan.  The  purpose 
of  the  forward  curvature  at  the  lip  of  the  blade  is  to  cause 
the  air  entering  in  a  radial  direction  to  slide  along  the  blade 
without  shock.  The  air  is  thus  deflected  from  a  radial  path 
and  given  the  necessary  motion  of  rotation  without  undue 
loss  of  power.  Experiments  performed  on  fans  in  which 
the  tips  of  the  blades  were  bent  forwards  in  the  direction  of 
rotation  showed  an  increase  in  the  pressure,  but  a  larger 
decrease  in  the  quantity  of  air  produced  per  unit  of  power 
and  a  consequent  decrease  of  efficiency.  The  forward  cur- 
vature of  the  blade,  whether  at  the  inner  or  outer  end  of 
the  blade  is  sometimes  spoken  of  as  the  cupping  of  the  blade. 

40.  Inclination  of  Blades. — In  some  fans,  the  blades 
are  flat,  but  are  set  in  an  inclined  position,  so  that  the  blade 
makes  an  angle  with  a  radial  line.  This  construction  is  typ- 
ical of  the  Guibal  fan.  The  inclination  of  the  blade  in  this 
case  is  always  backwards  from  the  direction  of  motion,  and 


§15  MINE  VENTILATION  41 

its  effect  is  the  same  as  has  just  been  described  in  reference 
to  the  backward  curvature  of  blades. 

41.  Tapered  Blades. — In  some  types  of  fans,  such  as 
the  Waddle   and  the   Schiele   fans,  the  blades  are  tapered, 
that  is,  the  width  of  the  blade  a  decreases  from  its  inner 
toward  its  outer  diameter,  either  in  a  curve  cb  as  shown  in 
Fig.  19,  or  in  a  straight  line.     The  purpose  of  this  is  to 
maintain  a  uniform  area  of  passage  through  the  fan.     Since 
th?s  area  of  passage  at  any  point  in  the  fan  is  equal  to  the 
product  of  the  circumference  of  a  circle  of  the  fan  drawn 
through  that  point  and  the  width  of  the  blade  at  that  point, 
it  follows  that  the  width  of  the  blade  should  decrease  as  the 
radius  of  the  circle  increases,  in  order  to  main- 
tain a  constant  area  of  passage  for  the  air. 

For  example,  if  the  width  of  a  fan  blade  at  the 
throat  of  the  fan  is  4  feet,  the  diameters  of  the 
inner  and  outer  circles  of  the  fan  being  10  feet 
and  16  feet,  respectively,  the  required  width  of 
the  blade  at  its  tip  is  b  =  4i  X  4  =  2.5  feet. 
The  maintaining  of  a  constant  area  of  passage 
through  the  fan  prevents  the  possibility  of  eddies 
within  the  fan  due  to  the  expansion  of  area.  It,  however, 
presents  a  disadvantage  of  decreasing  the  volume  of  the  fan 
that  more  than  offsets  the  advantages  gained.  The  curved 
edge  be  is  not  an  essential  feature  of  a  tapered  blade, 
but  is  characteristic  of  the  blades  of  the  Schiele  fan.  This 
edge  may  be  straight  instead  of  curved. 

42.  Guide  Blades. — In  some  fans,  as  for  instance  the 
Capell,  blades  are  used  outside  the  fan  casing  in  order  to 
gather  the  air  into  the  intake.     Interior  guide  blades  are 
also  sometimes  used,  as  in  the  case  of  the  Capell  fan,  Fig.  16, 
to  deflect  the  air-current  from  the  intake  to  the  regular  radial 
blades;  or  instead  of  extra  blades  of  this  character,  a  cone  is 
sometimes  used,  as  in  the  case  of  the  Robinson  fan,  Fig.  17, 
or  as  shown  in  Figs.  5  and  10. 


42  MINE  VENTILATION  §15 

FAN    CALCULATIONS 

43.  Calculation  of  Water  Gauge  Due  to  Action  ol 
Fan. — The  method  that  has  been  employed  for  calculating 
the  water  gauge  any  given  fan  may  produce  at  a  given  speed 
is  based  on  the  theoretical  height  of  air  column  or  head  due  to 
the  tangential  velocity  of  the  fan.  The  tangential  velocity  of 
a  fan  is  the  velocity  of  the  blade  tips  and  is  usually  measured 
in  feet  per  second.  This  velocity  is  also  often  called  the 
Peripheral  velocity  or  peripheral  speed,  and  is  then  measured 
in  feet  per  minute.  For  example  it  is  often  stated  that 
experience  has  shown  that  the  peripheral  velocity  of  the 
Guibal  fan  giving  the  best  results  varies  from  5,000  feet 
to  6,000  feet  per  minute,  corresponding  to  a  tangential 
velocity  of  about  80  to  100  feet  per  second.  The  following 
formula  is  used  to  calculate  the  theoretical  height  of  air 
column  due  to  a  tangential  speed  of  fan  equal  to  vt  feet 
per  second: 

*~7  (1) 

in  which  h  =  height  or  head   of   air  column  of   the   same 

density  as  the  flowing  air,  in  feet; 
vt  =  tangential  velocity  of  fan,  in  feet  per  second; 
g  =  acceleration  due  to  gravity  in  feet  per  second, 

32.16  feet. 

The  theoretical  water  gauge  produced  by  a  centrifugal  fan 
having  a  tangential  speed  vt  is  derived  by  multiplying  the 
head  of  air  column  in  this  formula  by  12,  to  reduce  it  to  inches, 
and  this  result  by  the  ratio  of  the  weight  of  air  to  the  weight 
of  an  equal  volume  of  water — this  ratio  for  average  con- 

1  2 

ditions  is  approximately  — j—.     Hence,  the  formula  express- 
1,000 

ing  the  theoretical  water  gauge  /  for  a  centrifugal  fan  at  any 
given  speed  vt  is, 

/  _  V*'  v  L2  X  12  (Q\ 

~7    Tooo" 

The  head  of  air  column  and  the  water  gauge  expressed  by 
these  two  formulas  are  purely  theoretical  values  based  on  the 


§15  MINE  VENTILATION  43 

assumption  that  the  air  is  received  into  the  fan  and  dis- 
charged without  shock,  the  velocity  of  discharge  being  zero. 
The  formulas  are  theoretically  incomplete  since  they  do  not 
consider  the  resistance  against  which  the  fan  is  operated.  It 
is  important  to  remember  that,  practically,  the  pressure  and 
water,  gauge  produced  by  a  fan  are  not  due  to  the  size  or 
speed  of  the  fan,  but  are  determined  by  the  resistance  of  the 
airway  to  which  the  fan  is  connected.  The  same  fan  at  the 
same  speed  will  produce  a  different  pressure,  according  to 
the  resistance  against  which  it  is  operated.  For  this  reason, 
the  peripheral  speed  of  a  centrifugal  fan  is  not  a  true  indica- 
tion of  the  pressure  produced;  it  is  rather  an  index  of  the 
power  consumed  in  turning  the  ventilator.  Other  condi- 
tions being  the  same,  the  same  power  must  be  applied  to 
a  ventilator  to  produce  a  given  peripheral  speed  under  all 
conditions  of  resistance,  but  the  pressure  and  the  velocity 
produced  depend  on  the  resistance  against  which  the  venti- 
lator works.  The  quantity  of  air  produced  depends  on  the 
velocity  of  the  air-current  in  the  airway  and  the  sectional 
area  of  the  airway. 

EXAMPLE.— Find  the  theoretical  water  gauge  that  may  be  produced 
by  a  fan  20  feet  in  diameter  revolving  at  a  speed  of  75  revolutions  per 
minute. 

SOLUTION. — The  tangential  velocity  of  this  fan  at  the  given  speed  is 
found  by  multiplying  the  circumference  of  the  fan  by  .the  number  of 
revolutions  per  minute  and  dividing  by  60;  thus, 

3.1416  X  20  X  75 
vt  =  —     — gQ —     —  =  78.54  ft.  per  sec. 

Then,  substituting  values  in  formula  2,  the  theoretical  water  gauge 
due  to  this  fan  at  the  given  speed  is 
78.54*      1.2  X  12 


The  speed  of  revolution  of  a  fan  may  vary,  although  the 
steam  pressure  on  the  engine  remains  constant.  This  will 
be  caused  chiefly  by  an  increase  or  decrease  of  the  mine 
resistance,  although  a  variation  in  the  readings  of  the  barom- 
eter and  thermometer  may  cause  a  slight  variation  in 
speed.  If  the  doors  separating  the  downcast  and  upcast  are 
left  open,  the  air-current  will  be  short-circuited  and  the 


44  MINE  VENTILATION  §15 

resistance  reduced.  This  increases  the  amount  of  air  pass- 
ing through  the  fan  and  increases  the  resistance  within  the 
fan,  causing  it  to  slow  down. 

44.  Manometrlcal  Efficiency. — The  manometrical 
efficiency  of  a  fan  is  the  ratio  of  the  actual  water  gauge 
produced  by  a  fan  at  a  given  speed  to  the  theoretical  water 
gauge  at  that  speed,  as  calculated  by  formula  2  in  Art.  43. 
This  term  is,  therefore,  rapidly  being  given  up,  as  it  does 
not  express  the  efficiency  of  the  fan  working  under  all  con- 
ditions, but  depends  on  the  resistance  of  the  airway  in  any 
given  case. 

Since  a  fan  running  at  a  given  speed  will  produce  a  water 
gauge  depending  on  the  resistance  of  the  airway,  a  fan  may 
give  a  manometrical  efficiency  of  50  per  cent,  at  one  mine 
and  only  40  per  cent,  manometrical  efficiency  at  another 
mine. 

EXAMPLE. — The  water-gauge  reading  taken  from  the  fan  drift  at 
the  top  of  a  shaft  is  2  inches;  the  fan  is  10  feet  in  diameter  and  is  run- 
ning at  a  speed  of  160  revolutions  per  minute.  What  is  the  mano- 
metrical efficiency  of  this  fan  at  the  given  speed  in  this  case? 

SOLUTION.— The  tangential  velocity  of  the  fan  at  this  speed  is 
3.1416  XO  X  160 


60       - 

Substituting   values  in   formula  2  of  Art.  43  for  the  theoretical 
water  gauge,  at  this  speed  of  the  fan, 

'      83.78*^  1.2  X  12  =  3<14.n> 


32.16 

The  actual  water  gauge  being  2  inches,  the  manometrical  efficiency  in 
this  case  is 

K  =  -|^p  =  63.69  per  cent.     Ans. 

45.     Static    Pressure    Due    to    a    Centrifugal    Fan. 

Air  being  a  compressible  fluid  is  subject  to  what  may  be 
called  a  kinetic  condition  whenever  the  continuous  flow  of  the 
air  is  interrupted.  For  a  steady  flow,  the  pressure  producing 
the  flow  is  constant,  but  any  change  in  the  velocity  of  the 
flowing  air  or  interruption  of  the  steady  flow  causes  an 
increase  in  the  pressure  for  all  velocities  less  than  twice  the 
acceleration  due  to  gravity  (1  g  =  64.32  feet  per  second) 


§15  MINE  VENTILATION  45 

and  a  decrease  in  the  pressure  for  all  velocities  greater  than 
this.  Practically,  this  condition  may  be  expressed  by  the 
formula, 


in  which  ps  =  static  pressure,  in  pounds  per  square  foot; 

p  —  pressure    due   to   velocity  v,   in   pounds   per 

square  foot; 
v  =  velocity  in  open  airway  for  same  power,  in 

feet  per  second; 

g  =  acceleration  due  to  gravity,  in  feet  per  second. 
The  same  formula  will  apply  when  the  pressure  is  expressed 
in  inches  of  water  gauge,  as  in  the  following  example: 

EXAMPLE.  —  If  a  certain  fan  produces  an  actual  water  gauge  of 
3.1  inches  at  a  speed  of  200  revolutions  per  minute,  the  velocity  of  the 
air  in  the  fan  drift  being  2,400  feet  per  minute  (40  feet  per  second), 
.what  will  be  the  static  gauge  produced  by  this  fan  at  the  same  speed? 
SOLUTION.  —  Here  the  pressure  is  expressed  in  inches  of  water  gauge. 
Substituting  values  in  the  formula  for  the  static  gauge  of  this  fan  at 
the  given  speed, 

ps  =  2(3^Q16)  x  3.1  =  4.98,  say  5  in.     Ans. 

If  the  velocity  of  the  air-current  in  the  fan  drift  in  the 
example  had  been  64.32  feet  per  second  instead  of  40  feet 
per  second,  the  static  gauge  when  the  fan  drift  was  closed 
would  have  been  the  same  as  the  working  gauge  when  the 
fan  drift  was  open.  On  the  other  hand,  if  the  conditions  were 
such  as  to  make  the  velocity  of  the  air-current  in  the  open 
drift  greater  than  64.32  feet  per  second,  the  static  water  gauge 
when  the  drift  was  closed  would  be  less  than  the  working 
gauge  for  an  open  drift. 

46.  Mechanical  Efficiency  of  Fan.  —  The  term 
mechanical  efficiency  of  a  fan  should  mean  the  ratio  of 
the  effective  work  performed  on  the  air  per  minute  (that  is, 
the  power  on  the  air  as  determined  from  any  of  the  formulas 
for  h  or  u  given  in  Mine  Ventilation,  Part  1)  to  the  work  per 
minute  or  the  power  delivered  to  the  fan  shaft  by  the  engine. 
The  method  usually  employed  in  practice  for  finding  the 
mechanical  efficiency  of  a  fan  is  such  that  the  results  express 


46  MINE  VENTILATION  §15 

the  combined  efficiencies  of  the  fan'  and  engine  or  other  motor 
operating  the  fan  instead  of  the  efficiency  of  the  fan  alone. 
This  difference  may  be  of  considerable  importance;  for 
example,  the  efficiency  of  an  engine  may  be  low,  while  the 
efficiency  of  the  fan  operated  by  this  engine  may  be  high;  in 
this  case,  the  combined  efficiency  of  the  fan  and  engine  would 
be  considerably  lower  than  the  efficiency  of  the  fan  alone. 
.Much  depends,  therefore,  on  the  efficiency  of  the  engine 
driving  the  fan  if  this  efficiency  is  included  in  the  efficiency 
of  the  fan.  Unless  the  efficiencies  of  the  fan  and  engine  are 
separate,  there  can  be  no  true  comparison  of  ventilators 
driven  by  different  engines  or  even  of  the  same  fan  when 
driven  at  different  speeds,  as  the  maximum  efficiency  of  the 
fan  may  be  obtained  at  a  certain  speed  and  the  maximum 
efficiency  of  the  engine  at  a  different  speed. 

To  avoid  confusion  as  to  what  is  meant  by  the  term  effi- 
ciency whenever  the  efficiency  of  a  machine  is  given,  it  should 
be  accompanied  by  a  clear  statement  of  exactly  what  the  term 
means.  The  efficiency  of  a  machine  depends  on  the  speed 
and  the  conditions  under  which  the  machine  operates,  and  the 
maximum  efficiency  should  be  obtained  when  the  machine  is 
operated  at  the  speed  for  which  it  was  designed.  In  the  case 
of  a  fan,  the  speed  at  which  the  fan  is  designed  to  be  oper- 
ated should  correspond  to  the  average  working  conditions 
under  which  the  mine  must  be  ventilated,  although  in  the 
early  development  of  the  mine  the  actual  speed  of  the  venti- 
lator may  be  less  than  this,  and  in  emergencies  the  fan  may 
be  operated  at  higher  speeds;  the  efficiency  will  probably  be 
less  in  either  case  than  at  the  speed  for  which  the  fan  was 
designed. 

47.     Determination    of    Mechanical    Efficiency. — A 

new  fan  should  be  operated  for  at  least  10  days  or 
2  weeks  before  a  test  is  made  to  determine  its  efficiency 
so  as  to  insure  as  nearly  as  possible  the  actual  working 
condition  of  the  machinery  when  the  test  is  made. 

In  making  the  test,  the  fan  should  be  run  at  different 
speeds.  While  the  observations  are  taken  at  different 


§15  MINE  VENTILATION  47 

speeds  of  the  fan,  preference  and  special  attention  should 
be  given  to  that  speed  for  which  the  ventilator  was  designed. 
At  each  speed,  the  following  observations  should  be  taken: 
Indicator  cards  to  determine  the  power  of  the  engine,  readings 
of  the  barometer,  thermometer,  water  gauge,  and  anemometer 
to  determine  the  quantity  and  pressure  of  the  air  furnished 
by  the  fan. 

Indicator  cards  should  be  taken  from  the  engine  by  some 
one,thoroughly  familiar  with  such  work,  and  as  is  explained, 
in  detail,  in  Steam  Engines,  and  at  the  same  time  as  the  other 
observations  are  taken  in  the  fan  drift  and  elsewhere.  The 
barometer  should  be  read  at  regular  intervals  throughout 
the  test  to  determine  the  atmospheric  pressure. 

Whenever  practicable,  the  water-gauge,  thermometer,  and 
anemometer  readings  should  be  taken  in  the  fan  drift  at  a 
distance  from  the  fan  sufficient  to  avoid  the  oscillations  in 
the  air  that  would  render  the  observations  unreliable.  When 
the  observations  can  not  be  taken  in  the  fan  drift,  they  may 
be  taken  in  the  mine  at  the  first  break-through  or  cross-cut 
between  the  main  intake  and  main  return  airways,  but,  it 
will  then  be  necessary  to  allow  for  the  natural  air  column  in 
the  shaft  or  slope  if  such  column  exists  and  for  the  absorp- 
tion of  power  between  the  point  of  observation  and  the  ven- 
tilator. Wherever  taken,  it  is  absolutely  necessary  that  the 
anemometer,  water-gauge,  and  thermometer  readings  should 
be  taken  at  the  same  point  in  the  fan  drift  or  the  mine  air- 
ways and  that  they  be  taken  simultaneously  with  indicator 
cards  from  the  engine.  When  the  water-gauge  reading  is 
taken  in  the  fan  drift,  the  gauge  is  preferably  located  out- 
side of  the  drift  wall,  a  pipe  being  inserted  in  the  wall 
through  an  opening  that  is  carefully  sealed  around  the  pipe 
after  it  is  inserted.  The  pipe  should  extend  to  the  center  of 
the  fan  drift  and  the  end  of  the  pipe  should  not  be  directed 
either  against  or  in  the  direction  of  the  passing  current,  but 
the  opening  at  the  end  of  the  pipe  should  be  parallel  to  the 
direction  of  the  current.  To  avoid  any  undue  pressure  or 
suction  due  to  the  velocity  of  the  current  at  this  point,  the 
end  of  the  pipe  should  be  cut  square,  and  may  be  covered 


48  MINE  VENTILATION  §15 

with  a  flat  plate  of  sheet  iron  6  to  8  inches  square  firmly 
secured  to  the  end  of  the  pipe  so  that  the  plane  of  the 
plate  will  correspond  with  the  direction  of  the  current.  All 
volumes  of  air  must  be  calculated  for  the  same  temperature 
and  atmospheric  pressure;  hence,  it  is  necessary  to  take  the 
readings  of  the  thermometer  and  barometer  at  the  same 
time  as  the  other  readings. 

The  power  calculated  from  the  several  indicator  cards 
taken  from  the  engine  will  show  the  total  power  consumed 
in  the  operation  of  the  engine  and  the  fan  combined,  at  the 
time  of  making  each  test.  The  unit  of  ventilating  pressure, 
as  calculated  from  the  reading  of  the  water  gauge,  multiplied 
by  the  quantity  of  air  passing  the  point  of  observation,  as 
calculated  from  the  anemometer  readings  and  the  sectional 
area  of  the  passageway  at  this  point,  makes  known  the  power 
on  the  air,  or  the  effective  power.  The  ratio  of  this  effect- 
ive power  to  the  total  power  consumed  in  driving  the  engine 
and  the  fan,  multiplied  by  100,  gives  the  percentage  of  the 
combined  efficiencies  of  the  fan  and  engine  for  the  speed  at 
the  time  of  observation. 

48.  It  will  be  possible  to  determine  the  efficiency  of  the 
ventilator  separate  from  that  of  the  engine  only  when  the  fan 
can  be  disconnected  from  the  engine.  When  this  can  be 
done,  the  best  method  to  adopt  is  to  employ  a  device  such 
as  the  Prony  brake,  and  to  run  the  engine  at  practically  the 
same  speed  and  under  the  same  conditions  with  respect  to 
the  steam  pressure  and  other  details  that  go  to  make  up  the 
power  and  resistances  of  the  engine  and  its  load,  respectively. 
Under  these  conditions,  the  Prony  brake  has  virtually 
replaced  the  ventilator  as  far  as  the  load  on  the  engine  is 
concerned,  and  it  is  possible  then  to  estimate  the  load  due  to 
the  ventilator  at  this  speed  of  the  engine.  Indicator  cards 
are  taken  for  each  speed  of  the  engine  when  running  under 
the  load  due  to  the  ventilator,  and  these  are  compared  with 
corresponding  cards  taken  when  the  ventilator  has  been 
replaced  by  the  brake.  It  is  necessary  to  make  this  com- 
parison in  order  to  make  certain  that  the  power  of  the  engine 


§15  MINE  VENTILATION  49 

is  the  same  in  each  case,  or  to  reduce  the  results  to  a  com- 
mon basis  of  power.  It  would  not  be  sufficient  to  dis- 
connect the  fan  and  run  the  engine  at  the  same  speed  but 
under  no  load,  as  this  would  alter  the  frictional  resistances 
of  the  engine. 

In  estimating  the  efficiency  of  the  ventilator  separate  from 
that  of  the  engine,  the  load  due  to  the  ventilator,  as  deter- 
mined by  the  Prony  brake  for  any  given  speed,  is  taken  as 
the  net  power  delivered  by  the  engine  to  the  fan  shaft. 
Dividing  the  power  on  the  air  in  the  fan  drift  by  this  net 
power  delivered  to  the  fan  shaft  and  multiplying  by  100  will 
give  the  percentage  of  efficiency  of  the  fan  alone. 

It  is  not  usually  convenient  or  practicable  to  use  the  Prony 
brake  or  a  similar  device  in  testing  a  mine  fan  at  the  mine, 
consequently  the  mechanical  efficiency  usually  includes  the 
efficiency  of  both  the  fan  and  the  engine,  the  engine  being 
considered  as  a  part  of  the  fan. 

49.  Effect  of  Mine  Resistance  on  Mechanical  Effi- 
ciency of  a  Ventilator. — The  air-current  produced  by  a  fan 
must  pass  through  the  fan  itself  and  the  fan  like  any  other 
air  passage  offers  a  resistance  to  the  passage  of  the  air.  A 
portion  of  the  power  of  the  fan  is  thus  absorbed  within  itself, 
and  is  lost  as  far  as  the  ventilation  of  the  mine  is  concerned. 
The  resistance  of  a  fan  to  the  passage  of  air  through  it  is 
due  to  the  friction  of  the  air  against  itself  and  against  the  sur- 
faces of  the  fan  and  the  necessary  deflection  of  the  current 
through  the  various  passages  of  the  fan.  The  power  lost  in 
the  fan  may  be  assumed  as  proportional  to  the  cube  of  the 
quantity  of  air  passing,  and  may  be  expressed  by  the  formula, 

«.'«•**•  (1) 

in  which  #,  =  power  lost  in  the  fan,  in  foot-pounds  per  minute; 
£»  =  constant  for  the  particular  fan; 
q  •=  quantity  of  air  entering  the  fan,  in  cubic  feet 

per  minute. 
The  formula  for  the  power  on  the  air,  as  given  in  Mine 

Ventilation,  Part  1,  is  u  = 


50  MINE  VENTILATION  §15 

Letting    U  =  net  power  applied  to  the  fan  shaft,  in  foot- 

pounds per  minute; 
K  =  efficiency  of  the  fan; 

K  U  =  effective  power  or  the  power  on  the  air,  in 
foot-pounds  per  minute; 


then, 

a 

which  gives  for  the  power  applied  to  the  fan  shaft, 


K  a 

The  effective  power  or  the  power  exerted  on  the  air  by  the 
action  of  the  fan  is  equal  to  the  net  power  applied  to  the  fan 
shaft  less  the  power  absorbed  within  the  fan.  If  the  effi- 
ciency of  the  fan  be  taken  as  the  ratio  of  the  effective  power 
to  the  net  power  applied  to  the  fan  shaft,  the  efficiency  of  the 
ventilator  is  given  by  the  formula, 


Now  dividing  formula  1  by  formula  2,  member  by  member, 
we  have  for  the  ratio  of  the  power  lost  in  the  fan  to  the  net 
power  applied  to  the  fan  shaft, 


U       k±£  ks 

Ka* 

Substituting  this  value  in  formula  3,  and  solving  with 
respect  to  K,  the  efficiency  of  a  fan  when  producing  a  given 
circulation  is  given  by  the  formula, 

A-_»-£^ 

ks 
transposing  and  reducing, 

A-=  -  L-;  (5) 

l  +  ,.f 
ks 

Since  the  value  of  the  constant  d  is  expressed  by  a  small 

decimal,  while  the  value  of  the  expression     _  .  =  Xu  is  large 

Vks 

and  unwieldy,  the  above  formula  is  improved  by  adopting 
for  this  constant  the  value  ct  =    -~,  which  gives  a  more 


§15  MINE  VENTILATION  51 

convenient  value.     The  formula  for  the  efficiency  of  the  ven- 
tilator in  terms  of  the  circulation  then  becomes 


The  value  of  the  factor  c  is  practically  constant  for  the 
same  type  of  fan,  and  therefore  this  may  be  called  the  fan 
constant. 

It  will  be  observed  from  the  above  reasoning:  that  a  venti- 
lating fan  may  have  a  different  efficiency  when  circulating 
air  in  different  mines  or  airways.  In  other  words,  the 
efficiency  of  a  fan  depends  not  only  on  the  fan  itself,  but  also 
on  the  mine  resistance  with  which  it  is  connected.  This  is 
due  to  the  fact  that  for  any  given  power  applied,  the  mine 
resistance  determines  the  quantity  of  air  in  circulation, 
and  this  quantity,  in  turn,  determines  the  power  lost  in  the 
ventilator,  and  the  efficiency  of  the  machine. 

50.  Equivalent  Orifice.  —  If  a  thin  plate  with  an  open- 
ing in  it  is  placed  across  the  path  of  an  air-current,  a  certain 
resistance  will  be  offered  to  the  passage  of  the  current  and 
the  amount  of  resistance  will  depend  on  the  size  of  the 
opening.  The  resistance  offered  by  such  an  opening  to  the 
flow  of  an  air-current  through  it  is  equal  to  the  resistance 
offered  by  a  certain  amount  of  rubbing  surface  in  a  mine  to 
the  flow  of  the  same  air-current  through  the  mine.  Daniel 
Murgue  some  years  ago  proposed  expressing  the  resistance 
of  any  mine  by  the  size  of  the  orifice  in  a  thin  plate  that  will 
produce  a  resistance  equal  to  the  resistance  of  the  mine  when 
a  current  is  flowing  under  a  certain  head.  >,  This  orifice  he 
calls  the  equivalent  orifice.  The  term  equivalent  orifice  has 
been  used  by  many  writers,  particularly  in  connection  with 
fan  tests,  to  compare  the  work  of  different  fans,  as  the  work 
done  by  each  fan  can  by  this  means  be  compared. 

The  formula  for  the  equivalent  orifice  is  determined  as 
follows:  The  velocity  of  the  flow  of  a  fluid  through  an  orifice 
is  given  by  the  formula, 

(1) 


52  MINE  VENTILATION  '  §15 

in  which  v  =  velocity  of  air,  in  feet  per  second; 

g  =  acceleration   due    to    gravity,    32.16    feet    per 

second; 
h  =  head,    in    feet    of    air    column    producing    the 

velocity. 

Multiplying  both  sides  of  this  equation  by  A,  the  area  of 
the  equivalent  orifice, 

A  v  =  A  V2  gh 
then,  since  q  =  A  v,  q  =  A  ^gh,  and 

A  =  -3=  (2) 


When,  a  fluid  flows  through  an  orifice  in  a  thin  plate,  the 
stream  is  contracted  a  short  distance  beyond  the  orifice,  but 
soon  expands  again  to  the  full  size  of  the  orifice.  The  con- 
traction is  called  the  contracted  vein  or  vena  contracta.  In 
consequence  of  this  contraction,  the  velocity  of  flow  through 
the  orifice  is  reduced  from  the  theoretical  amount,  and  for  air 
it  is  assumed  as  from  .62  to  .65  of  the  theoretical  value.  On 
account  of  the  vena  contracta,  the  area  of  the  orifice  must  be 
correspondingly  increased.  Using  decimal  .62,  this  formula 
becomes 

A= 2=  (3) 

Al^gh 

Reducing  this  formula  to  cubic  feet  per  minute  and  inches 
of  water  gauge,  the  equation  for  the  equivalent  orifice  is 

A  =  .00038  X  -2=          (4) 

Vz 

51.  Advantages  of  Centrifugal  Fans. — The  centrif- 
ugal fan  is  the  most  reliable  of  all  the  ventilating  motors 
used  in  mining  work  because  its  action  is  more  constant  and 
more  readily  controlled  than  that  of  any  other  kind  of 
ventilator.  Mining  work  often  requires  a  sudden  increase 
of  the  ventilating  power,  and  in  the  use  of  the  fan  this  can 
be  done  at  once  by  increasing  the  speed  of  the  fan.  Other 
ventilating  motors,  as  the  furnace  or  the  steam  blast,  are 
capable  in  most  cases  of  producing  but  a  slow  and  very 
limited  increase  in  the  quantity  of  air  circulated.  The  cost 


§15  MINE  VENTILATION  53 

of  running  a  fan  is  much  less  than  that  of  running  a  furnace 
for  the  same  circulation,  and  there  is  not  the  same  danger 
of  fire  in  the  operation  of  a  fan  as  in  the  use  of  a  furnace. 
A  ventilating  fan  at  a  mine  is  quite  frequently  arranged  so 
that  the  ventilating  current  in  the  mine  may  be  reversed  by 
opening  and  closing  doors  made  for  that  purpose.  While  it 
is  possible  to  arrange  a  furnace  in  a  like  manner,  this  is  not 
done,  for  the  reason  that  the  doors  controlling  such  a  change 
of  the  ventilating  current  would,  in  the  case  of  a  furnace,  be 
located  in  the  mine  and  would  be  destroyed  or  difficult  to 
reach  in  case  of  an  accident  requiring  the  current  to  be 
changed, 

52.  Efficiency  of  Mine  Furnace  Compared  With 
Fan. — Previous  to  the  general  adoption  of  the  centrifugal  fan 
as  a  mine  ventilator,  the  mine  furnace  was  very  generally 
used,  and  in  the  case  of  deep  shafts  it  was  for  a  long  time 
held  to  be  better  adapted  to  the  ventilation  of  mines  than 
any  other  means  of  ventilation,  though  the  fan  was  admitted 
to  be  better  adapted  for  shallow  shafts  than  a  furnace.  This 
view  of  the  relative  efficiency  of  the  furnace  and  the  fan  in 
deep  mining  was  supported  by  the  fact  that  as  the  depth  of 
the  mine  below  the  surface  increased  the  power  of  the  fur- 
nace was  increased  in  the  same  proportion,  while  on  the 
other  hand,  in  fan  ventilation  the  increase  in  the  depth  of 
the  shaft  caused  no  increase  of  power  but  an  increase  of 
resistance  due  to  the  shafts  through  which  the  entire  current 
of  air  must  pass. 

The  work  of  a  mine  furnace  is  best  compared  with  that  of 
a  fan  on  the  basis  of  their  respective  powers.  It  has  been 
explained  that  the  pressure  due  to  a  mine  furnace  under 
ordinary  conditions  is  dependent  on  the  depth  of  the  furnace 
shaft,  while  the  power  is  determined  by  the  depth  of  the 
shaft  and  the  mine  resistance.  For  the  same  furnace,  there- 
fore, the  power  will  vary  as  the  resistance  of  the  mine 
varies,  the  power  decreasing  as  the  resistance  increases, 
thus  making  the  furnace  less  efficient  as  the  development 
of  the  mine  increases,  except  as  recourse  is  had  to  splitting 


54  MINE  VENTILATION  §15 

the  air-current  and  thereby  increasing  the  volume  of  the  air 
in  circulation  and  the  power  of  the  furnace. 

It  must  be  remembered  that  the  power  of  a  furnace  is 
wholly  effective  in  producing  the  circulation  of  air  in  the  mine. 
Hence,  in  comparing  a  mine  furnace  with  a  ventilating  fan, 
the  power  of  the  furnace  must  be  divided  by  the  general 
efficiency  of  a  ventilating  fan  in  order  to  find  the  gross 
power  of  the  fan  that  will  give  the  same  effective  power,  in 
the  mine  as  is  given  by  the  furnace.  Suppose  that  the 
power  of  a  furnace  producing  75,000  cubic  feet  of  air  in  a 
certain  mine  at  a  depth  of  1,500  feet  below  the  surface  was 
found  to  be  109.454  horsepower.  Assuming  the  general 
efficiency  of  a  ventilating  fan  to  be  60  per  cent.,  the  gross 
power  of  a  fan  producing  the  same  power  on  the  air  as  this 

furnace  will  be  !P_?iiM  =  182+  horsepower.     A  fairly  good 
.60 

slide-valve  fan  engine  will  consume,  say  5  pounds  of  coal 
per  horsepower  per  hour,  making  the  total  coal  consumed  in 
this  case  182  X  5  =  910  pounds  per  hour.  It  may  be 
assumed  that  the  furnace  accomplishing  this  work  will  con- 
sume 2,700  pounds  of  coal  per  hour,  or  practically  three 
times  the  quantity  required  for  operating  a  fan. 

In  addition  to  the  increased  consumption  of  coal,  the 
furnace  requires  constant  attendance.  In  the  case  just  con- 
sidered, there  would  probably  be  required  two  furnaces  and 
the  constant  attention  -of  two  furnace  men  to  handle  this 
quantity  of  coal  and  keep  the  fire  in  good  condition. 


FUELS 

PROPERTIES    OF    FUELS 


COMPOSITION    AND    CLASSIFICATION 

1.  A  fuel  is  any  substance  that  is  burned  for  the  purpose 
of  generating  heat,  as  wood,  charcoal,  coal,  coke,  oil,  or  gas. 
It  is  composed  of  certain  elements,  such  as  carbon,  hydrogen, 
and  sulphur,  that  are  combustible  and  that  give  out  heat 
when  burned,  and  of  certain  impurities,  such  as  moisture  and 
ash,  that  detract  from  the  heating  value.     The  study  of  fuels 
involves  a  consideration    of   their   physical  characteristics, 
chemical   composition,   and   geographical    distribution,   also 
their  theoretical  and  practical,  or  available,  heating  values, 
and  the  chemical  theory  of  combustion. 

2.  Fuels  are  classified  as:   (1)  solid  fuels,  including  wood, 
charcoal,   coal,   coke,   and  peat;    (2)    liquid  fuels,   including 
petroleum     and    its     derivatives,    naphtha,    gasoline,    etc.; 
(3)  gaseous  fuels,  including  natural  gas,  and  various  manu- 
factured gases,  such  as  coal  gas,  water  gas,  producer  gas,  etc. 


COMBUSTIBLE    ELEMENTS 

3.  Carbon  is  the  principal  heat-giving  constituent  of  all 
fuels.  It  is  found  in  three  forms,  which  differ  greatly  in 
their  physical  properties  and  yet  are  the  same  chemically; 
viz.,  the  diamond  and  graphite,  which  are  crystalline  forms  of 
carbon;  and  amorphous  carbon,  which  is  not  crystallized. 
The  latter  form  is  the  chief  constituent  of  coal,  charcoal 

Copyrighted  by  International  Textbook  Company.    Entered  at  Stationers'  Hall,  London, 


2  FUELS  §  16 

coke,  etc.,  and  is  the  only  form  that  is  combustible  in  an 
ordinary  fire  and  of  value  as  a  fuel. 

4.  Hydrogen,  the  second  important  heat-giving  element 
contained  in  fuels,  exists  in  the  free,  or  uncombined,  state  in 
certain  manufactured  fuel  gases,  such  as  water  gas,  but  is 
more  commonly  combined  with  carbon,  as  a  hydrocarbon,  or 
with  oxygen  in  the  form  of  water. 

If  both  hydrogen  and  oxygen  exist  in  a  fuel,  it  is  assumed 
that  all  the  oxygen  is  combined  with  hydrogen  in  the  form 
of  water,  H*O.  The  hydrogen  thus  combined  has  no  fuel 
value  and  must  therefore  be  deducted  from  the  total  amount 
of  hydrogen  present  in  calculating  the  heating  value  of  the 
fuel.  The  hydrogen  left  after  deducting  what  is  combined 
with  oxygen  is  called  the  available  hydrogen.  Since  the 
weight  of  hydrogen  in  water  is  one-eighth  the  weight  of  the 
oxygen,  the  percentage  of  available  hydrogen  is  obtained 
by  the  formula, 

*.-*'-! 

o 

in  which    h  =  percentage  of  available  hydrogen  in  the  fuel; 
H  =  percentage  of  hydrogen  in  the  fuel; 
O  =  percentage  of  oxygen  in  the  fuel. 

EXAMPLE.— Find  the  amount  of  hydrogen  in  the  form  of  moisture 
and  the  amount  of  available  hydrogen  in  a  piece  of  dry  wood  that 
contains  50  per  cent,  of  carbon,  6  per  cent,  of  hydrogen,  42  per  cent, 
of  oxygen,  and  2  per  cent,  of  ash. 

SOLUTION.— Using  the  formula  h  =  H  -  -^,  we  have,  hydrogen  as 

O 

O         42 

moisture  =  —  =  —  =  5.25  per  cent.     Ans. 

O  O 

Available  hydrogen,  h  =  6  -  5.25  =  .75  per  cent.    Ans. 

It  is  evident,  therefore,  that  the  greater  the  amount  of 
oxygen  in  a  fuel,  the  less  will  be  its  heating  value. 

5.  Sulphur,  which  is  present  in  most  coals  and  in  some 
other  fuels  in  an  amount  ranging  from  .5  to  5  per  cent.,  is 
usually  combined  with  iron  as  iron,  sulphide  or  pyrites,  FeS,, 
and  its  presence  is  indicated  by  the  high  iron  content  of  the 
ash.     In  this  form,  1  pound  of  sulphur  has  about  one-half 


§  16  FUELS  3 

the  heating  value  of  1  pound  of  carbon.  The  sulphur  that 
exists  in  the  form  of  sulphates,  usually  as  calcium  sulphate 
or  sulphate  of  lime,  CaSOt,  has  no  heating  value. 

Sulphur  is  always  an  objectionable  element  in  coal,  since 
the  iron  with  which  it  is  usually  combined  is  one  cause  of 
the  troublesome  clinker  on  the  grates  of  furnaces.  When 
coal  is  used  for  smelting  or  heating  iron,  the  sulphur  is 
still  more  objectionable,  since  it  is  partly  absorbed  by  the 
iron  and  deteriorates  its  quality. 


IMPURITIES    IX    FUELS 

6.  Most  fuels  contain  varying  amounts  of  incombustible 
substances  that  may  be  regarded  as  impurities,  since  they 
detract   from    the    heating   value    of   the    fuel.     These    are 
oxygen,  which  is  combined  with  the  carbon  and  with  hydro- 
gen as  moisture;  nitrogen,  the  inert  chemical  element,  which 
is  found  in  a   small  percentage;    and  various  mineral  sub- 
stances, such  as  silica,  alumina,  iron,  and  lime,  which  com- 
pose the  ash  of  the  fuel.     Potash,  or  potassium  carbonate,  is 
a  large  constituent  of  the  ashes  of  wood  or  charcoal. 

7.  Moisture  is  contained   in  nearly  all   fuels.      A  part 
of  this  moisture  will  evaporate  if  the  fuel  is  exposed  to  the 
air,  but  a  part  can  be  driven  off  only  by  heating  the  fuel  at 
a  temperature   slightly  above  the    boiling  point  of    water. 
This  second  part  .is  called  hygroscopic  moisture.     Moisture, 
or  water,  in  a  fuel  has  no  heat  value  and  is  an  inert  con- 
stituent that  is  handled  and  finally  expelled  at  a  cost  of  fuel. 
Each  per  cent,  of  moisture  means  20  pounds  less  fuel  for 
each  ton  of  coal. 

8.  Ash  is  an  inert  constituent,  and  for  each  per  cent,  of 
ash  present  20  pounds  of  useless  weight  has  to  be  handled, 
and  there  is  a  loss  of  20  pounds  per  ton  of  fuel.     Water  in 
a  fuel  is   removed    at   the  cost  of   heat  of    the  fuel,  while 
ashes  are  removed  at  extra  cost  of  labor.     With  coal  at  $3 
per  ton  and  labor  at  $1  per  day,  it  is  estimated  that  if  the 
cost  of  stoking  the  coal  is  6f  per  cent,  of  the  cost  of  the 


4  FUELS  §  16 

coal,  and  cost  of  handling  ashes  is  double  that  of  stoking  the 
coal,  5  per  cent,  of  ash  will  lessen  the  fuel  value  of  the  coal 
over  6  per  cent.;  10  per  cent,  of  ash,  over  12  per  cent.;  and 
so  on.  Iron  in  a  fuel  gives  a  reddish  color  to  the  ash,  and 
the  intensity  of  the  color  of  the  ash  furnishes  a  rough  means 
to  estimate  the  amount  of  iron  contained  in  a  fuel.  Iron  in 
an  ash  makes  it  more  fusible  and  increases  its  tendency  to 
clinker.  In  domestic  consumption,  where  the  temperature  is 
low,  the  quantity  of  ash  is  of  more  importance  than  its  fusi- 
bility, but  for  steam  purposes,  where  high  temperature  is 
required,  ashes  of  a  clinkering  coal  will  fuse  into  a  vitreous 
mass  and  accumulate  on  the  grate  bars  and  exclude  the 
passage  of  air  necessary  for  combustion.  The  practicability 
of  employing  a  coal  will  often  be  determined  by  the  quality  of 
the  clinkering  of  the  ashes.  For  steam  purposes,  those  coals 
are  best  whose  ashes  are  nearly  pure  white  and  which  contain 
little  or  no  alkali  or  iron,  and  contain  only  silica  and  alumina. 


METHODS    OF   EXPRESSING    THE    COMPOSITION    OF   A   FUEL 

9.  Two  methods  of  analyzing  fuels  are  in  common  use, 
known  as  proximate  and  ultimate  analyses.     The  proximate 
analysis  determines  the  amounts  of  moisture,  volatile  matter, 
fixed  carbon,   and  ash  contained  in  the  fuel;    the  ultimate 
analysis  determines  the  amounts  of  the  elements,  carbon, 
hydrogen,  oxygen,  nitrogen,  and  sulphur  in  the  dry  fuel,  and 
the  amount  of  ash;  the  ash  may  be  analyzed  further,  if  neces- 
sary, to  determine  the  silica,  alumina,  iron,  etc.  contained  in  it. 

10.  In  making  a  proximate  analysis,  the  moisture  is  first 
driven  off  by  heating  the  sample  to  219°  to  225°  F.;   the 
volatile  matter  is  then  expelled  by  heating  to  a  red  heat 
without    access   of   air;    the  remainder  is    then  thoroughly 
burned  at  a  white  heat  by  the  aid  of  a  gentle  current  of  air 
or  of  oxygen  gas  until  nothing  but  the  ash  remains.     The 
detailed  method    of   making  a   proximate  analysis  will   be 
given  later.     The  proximate  analysis  thus   gives  the  four 
constituents — moisture,  volatile  matter,  fixed  carbon,  and  ash 
— and  the  sum  of  their  percentages  is  100.     If  the  content  of 


§16 


FUELS 


sulphur  is  desired,  it  is  determined  separately  by  the  methods 
of  ultimate  analysis.  It  is  also  sometimes  convenient  to 
consider  the  fuel  to  be  free  from  moisture  before  an  analysis 
is  made  and  to  express  its  composition  as  consisting  of 
volatile  matter,  fixed  carbon,  ash,  and  sulphur. 

In  some  cases,  the  amounts  of  fixed  carbon  and  volatile 
matter  are  expressed  as  percentages  of  the  total  combustible. 
Thus,  the  analysis  of  the  same  coal  may  be  expressed  by 
any,  of  the  following  forms: 


1.    ULTIMATE  ANALYSIS 

PER  CENT. 
Carbon      ......    76.10 

Hydrogen 4.89 

Oxygen 6.90 

Nitrogen 1.40 

Sulphur 1.96 

Ash 8.75 

100.00 

3.    PROXIMATE  ANALYSIS  OF 
SAMPLE  FREE  FROM  MOIS- 
TURE, OR  DRY  COAL 

PER  CENT. 
.    34.85 


2. 


PROXIMATE  ANALYSIS 
PER  CENT. 


Moisture  .  .  . 
Volatile  matter 
Fixed  carbon  . 
Ash  . 


Sulphur 


1.50 

34.33 

55.42 

8.75 

100.00 

1.96 


4.    ANALYSIS  OF  COM- 
BUSTIBLE 

PER  CENT. 
.    38.25 


Volatile  matter 
Fixed  carbon  . 
Ash  , 


Volatile  matter 
Fixed  carbon    . 


56.27 
8.88 


61.75 
100.00 


100.00 

Sulphur 1.99 

The  second  form  of  expressing  the  composition  is  the  one 
generally  used  for  coal  and  coke. 

11.  There  is,  unfortunately,  a  lack  of  uniformity  among 
chemists  as  to  the  method  of  reporting  a  proximate  analysis. 
The  percentages  of  moisture,  volatile  matter,  fixed  carbon, 
and  ash  should  be  reported  exactly  as  they  are  determined 
by  analysis  and  without  any  deductions  being  made  on 
account  of  the  amount  of  sulphur;  and  these  percentages 
should  add  up  to  100  per  cent.  The  sulphur,  which  is 
separately  determined  by  the  methods  used  in  ultimate 


6  FUELS  §  16 

analysis,  is  not  usually  included  in  the  total  of  100  per  cent. 
In  some  methods  of  reporting  analyses,  however,  the  sul- 
phur must  be  included  to  make  the  total  of  100  per  cent., 
because  the  sulphur  has  been  subtracted  from  the  fixed 
carbon  and  the  volatile  matter  as  found  in  the  proximate 
analysis,  one-half  from  each,  according  to  the  custom  of 
some  chemists,  or  .4  from  the  fixed  carbon  and  .6  from  the 
volatile  matter,  according  to  others.  The  common  practice 
now  is  to  report  the  fixed  carbon  and  the  volatile  matter  in  the 
figures  actually  obtained  by  the  proximate  analysis,  whether 
the  sulphur  is  determined  or  not.  Owing  to  the  different 
methods  of  reporting  proximate  analyses,  any  analysis  used 
in  a  calculation  must  be  first  examined  to  determine  on 
what  basis  the  fixed  carbon  and  volatile  contents  have  been 
reported. 

12.  To  reduce  the  figures  given  in  form  2,  Art.  10,  so 
that  the  analysis  will  be  for  a  sample  free  from  moisture, 
subtract  the  percentage  of  moisture  from  100  and  divide  the 
percentage  of  each  of  the  other  substances  by  this  difference; 
the  result  multiplied  by  100  will  be  the  percentage  of  each 
for  a  sample  free  from  moisture. 

EXAMPLE.  —  Express  analysis  2  so  that  it  may  be  for  a  sample  free 
from  moisture. 

SOLUTION.—  The  sample  dried  is  100  -  1.50  =  98.50  per  cent,  of  the 
original. 

Q4  qq  V  10ft 

—  =  34.85  per  cent,  volatile  matter 


55.42  X  100 

—  no  !^n  -  =  5t>-27  per  cent.  nx.ed  carbon 

=  8.88  per  cent,  ash 

I      Q£>    vx     ~lf\T\ 

-'  „„  gQ  —  =  1.99  per  cent,  sulphur.    Ans. 

13.  To  express  an  analysis  in  terms  of  combustible, 
divide  the  percentage  of  fixed  carbon  and  the  percentage  of 
volatile  matter,  as  given  in  the  proximate  analysis,  by  the 
sum  of  the  percentages  of  fixed  carbon  and  volatile  matter 
and  multiply  the  result  by  100,  similarly  to  the  method  used 
in  calculating  the  analysis  of  a  sample  free  from  moisture. 


§16  FUELS  7 

14.  -The  volatile  combustible  matter  is  that  part  of  a 
coal  that  is  driven  off  as  a  combustible  gas  when  the  coal  is 
heated  out  of  contact  with  oxygen.    When  a  large  percentage 
of  volatile  combustible  matter  is  present,  fuels  ignite  easily 
and  burn  with  a  long  yellow  flame,  and,  in  ordinary  combus- 
tion,  give  off  dense  smoke.     The   amount  of  the  volatile 
matter  in  a  coal  shows  approximately  whether  it  is  suitable 
for  the  manufacture  of  illuminating   gas,  but  it  tells  very 
little  as  to  the  quality  of  the  gas.     The  coking  of  coal  also 
is  dependent  to  some  extent  on  the  volatile  matter,  but  in 
just  what  manner  is  not  understood. 

15.  The   composition  of    the  volatile  matter  varies  in 
different    coals.     In    anthracite    and    semibituminous  coals, 
it  has  nearly  the  composition  of  marsh  gas  (methane),  C//«, 
and  it  then  has  a  heating  value  of  about  60  per  cent,  more, 
pound  for  pound,  than  that  of  carbon.     In  the  bituminous 
coals,  however,  the  volatile  portion  contains  more  or  less 
oxygen,  usually  combined  as  moisture,  the  quantity  varying 
greatly  in  different  coals,  but  usually  increasing  as  we  travel 
westwards   in    the  United   States.     In  such  cases,  the  fuel 
value  of  the  volatile  combustible  may  be  not  much  more 
than  half  that  of  carbon,  pound  for  pound. 

Too  much  stress  is  frequently  laid  on  the  fuel  value  of  the 
volatile  portion  of  a  fuel,  and  in  many  cases  through  careless 
firing  or  improper  furnace  construction,  little  of  the  theoret- 
ical calorific  power  of  the  volatile  combustible  matter  is 
obtained  in  the  furnace. 

16.  Fixed  carbon  is  the  carbon  that  exists  in  a  fuel  in 
the  solid  state  and  that  is  left  after  the  moisture  and  volatile 
part  of  the  fuel  are  driven  off  by  heating.    The  amount  of  fixed 
carbon  added  to  the  amount  of  ash  in  a  coal  gives  the  theo- 
retical amount  of  coke  obtainable  from  the  coal.    This  amount 
is  only  an  approximate  indication  of  the  amount  of  coke 
obtainable  in  the  coke  oven,  as  the  beehive  oven  produces 
less  than  the  theoretical  yield  and  the  by-product  oven  more. 

EXAMPLE. — A  certain  coal  has  the  following  analysis:  moisture, 
8  per  cent.;  volatile  matter,  36  per  cent.;  fixed  carbon,  46  per  cent.; 

14.3-23 


8  FUELS  §  16 

ash,  10  per  cent.;  what  is  the  analysis:  (a)  of  the  dry  coal?  (d)  of  the 
combustible? 

SOLUTION. — (a)  The  dry  coal  is  100  —  8  =  92  per  cent,  of  the  orig- 
inal; hence, 

Sfi  v  100 
the  volatile  matter  is        Q2        =  39.13  per  cent. 

fixed  carbon  is ^ —  =  SO-00  Per  cent. 

ash  is  — Q^ —  =  10.87  per  cent.     Ans. 

(f>)     The  combustible  is  100  -  (8  +  10)  =  82  per  cent,  of  the  original; 
hence, 

the  volatile  matter  is  36  *210°  =  43.90  per  cent. 

46  X  100 
fixed  carbon  is  — ^ —  =  56.10  per  cent.    Ans. 


SOLID  FUELS 


WOOD 

17.  Composition  of  Wood. — Wood  is  composed  of 
three  substances:  (1)  woody  fiber,  or  cellulose,  C,/iloOt, 
which  makes  up  the  chief  part  of  its  bulk;  (2)  the  constitu- 
ents of  the  sap;  (3)  water.  The  most  important  of  the  sap 
constituents  is  a  soluble  gum  (lignine)  amounting,  on  the 
average,  to  13  per  cent,  of  the  wood.  The  woody  fiber  and 
the  gum  of  the  sap  are  both  combustible,  while  the  water  is 
not  only  not  combustible,  but  its  evaporation,  while  the  wood 
is  burning,  absorbs  part  of  the  heat  and  detracts  from  the 
heating  value  of  the  other  constituents.  Dry  wood  is,  there- 
fore, a  better  fuel  than  undried  wood. 

Newly  felled  wood  contains  from  25  to  50  per  cent,  of 
water,  the  amount  varying  greatly  with  different  kinds,  but 
averaging  about  40  per  cent.  Exposed  to  the  air  at  ordinary 
temperatures,  wood  loses  a  large  part  of  its  moisture  and 
shrinks,  reaching  a  minimum  of  about  20  per  cent,  of  mois- 
ture after  about  2  years  of  air  drying,  but  it  absorbs  water 
and  swells  in  air  highly  charged  with  moisture. 


FUELS 


Ordinary  air-dried  wood  may  be  considered  as  having  the 
following  average  composition:  hygroscopic  water,  20  per 
cent.;  oxygen  and  hydrogen  in  the  proportion  in  which  they 
unite  to  form  water,  ff.,0,  40  per  cent.;  and  charcoal,  inclu- 
ding 1  per  cent,  of  ash,  40  per  cent. 

TABLE  I 


Kind  of  Wood 

Weight  of 
i  Cord 
Pounds 

Weight  of  Coal  Equiv- 
alent to  i  Cord 
of  Wood 
Pounds 

Hickory  or  hard  maple  .  .  . 
White  oak  

4,500 
7,8qo 

i,  800  to  2,000 

I,e4O  to   1,715 

Beach,  red  and  black  oak  .  . 
Poplar,  chestnut,  and  elm  .  . 
The  average  pine 

3,250 
2,350 
2,000 

1,300  to  1,450 
940  to  1,050 
800  to     925 

18.  Fuel  Value  of  Wood. — According  to  S.  P.  Sharp- 
less,  the  heating  value  of  perfectly  dry  wood  varies  from 
6,600  B.  T.  U.  per  pound  for  white  oak,  to  9,883  B.  T.  U.  for 
long-leaf  yellow  pine. 

The  weight  and  coal  equivalent  of  1  cord  of  different 
woods,  thoroughly  air-dried,  is  about  as  given  in  Table  I. 

TABLE   II 


Kind  of  Wood 

Composition 

Calorific  Value 

C 

H 

N 

0 

Ash 

Calories 

B.  T.  U. 

Oak  

50.16 

6.02 

.09 

43.36 

•  37 

4,620 

8,316 

Ash  

49.18 

6.27 

.07 

43.91 

•57 

4,7" 

8,480 

Elm  

48.99 

6.20 

.06 

44.25 

•  50 

4,728 

8,510 

Beech   .... 

49.06 

6.ii 

.09 

44.17 

•57 

4,774 

8,591 

Birch  •.    .    .    . 

48.88 

6.06 

.10 

44.67 

.29 

4,771 

8,586 

Fir                .    . 

CQ.  ^6 

c  02 

oc 

4-1     ?Q 

->a 

SO?  C 

9061 

Pine  

50.31 

6.20 

.04 

43.08 

•37 

5,085 

9,153 

10  FUELS  §16 

It  is  safe  to  assume  that  from  2i  to  2£  pounds  of  dry  wood 
is  equivalent  to  1  pound  of  average  quality  soft  coal  and  that 
the  fuel  value  of  the  same  weight  of  different  woods  is  very 
nearly  the  same;  that  is,  a  pound  of  hickory  is  worth  no 
more  for  fuel  than  a  pound  of  pine,  assuming  both  to  be  dry. 

In  Table  II,  Gottlieb  gives  the  values  for  the  composition 
and  calorific  values  of  different  varieties  of  wood. 

19.  Burning  of  Wood. — Wood  may  be  burned  without 
smoke  provided  that  there  is  an   ample   supply  of  highly 
heated  air.    If  a  small  stick  or  shaving  is  burned  in  the  open 
air,  the  flame  is  comparatively  cool  and  the  evaporation  of  the 
water  and  the  distillation  of  the  hydrocarbons  proceeds  slowly, 
so  that  each  particle  of  hydrocarbon  vapor  is  brought  in  con- 
tact with  highly  heated  air  and  burns  completely.     When 
burned  in  large  masses  in  a  furnace,  smoky  gas  is  first,  formed, 
and  this  must  later  come  in  contact  with  very  hot  air  in  order 
to  be  burned,  or  the  smoke  will  escape  from  the  chimney. 

An  experiment  made  with  a  narrow  strip  of  paper  (which 
is  made  from  wood  fiber)  shows  how  a  slight  change  in  the 
conditions  may  produce  a  smoky  or  a  smokeless  flame.  Roll 
the  paper  into  a  tube  i  inch  in  diameter,  and  holding  the 
tube  in  the  hand  light  one  end  of  it.  If  it  is  held  so  that 
the  lighted  end  is  the  higher,  the  volatile  matter  is  distilled 
slowly  and  little  or  no  smoke  is  produced;  but  if  inclined  so 
that  the  lighted  end  is  below,  it  will  burn  and  distil  the 
volatile  matter  rapidly,  and  a  column  of  smoke  will  escape 
from  the  unlighted  end. 

20.  In   burning  wood  in  furnaces,   a  large   combustion 
chamber    is  needed  to    insure    smokeless  combustion,   and 
provision  must  be  made  for  mixing  the  distilled  gases  with 
a  sufficient  quantity  of  hot  air  to  burn  them. 

21.  Sawdust,  straw,  wet  tan  bark,  and  bagasse  are 

often  used  as  fuel.  Wet  tan  bark  is  the  spent  tan  from 
tanneries.  Bagasse  is  the  refuse  of  sugar  cane  after  the  juice 
has  been  extracted.  These  fuels  are  practically  all  of  the 
same  composition  as  wood,  but  tan  bark  and  bagasse  may 
contain  from  50  to  60  per  cent,  of  water. 


§16  FUELS  11 

The  burning  of  wet  tan  bark  and  bagasse  can  be  success- 
fully accomplished  only  in  specially  constructed  firebrick  fur- 
naces with  large  combustion  chambers.  The  rate  of  feeding 
must  be  carefully  regulated  so  that  the  furnace  will  not 
become  chilled  by  an  excess  of  the  wet  fuel. 


CHARCOAL. 

22.  Charcoal  is  made  from  wood,  or  sometimes  peat, 
by  driving  off  the  volatile  portions  by  heat  and  leaving  the 
fixed  carbon  and  ash.     By  one  method  of  doing  this,  the 
wood  or  peat  is  piled  in  a  conical  heap  and  covered  over 
with  earth,  and  the  heat  for  driving  off  the  volatile  matter 
is  furnished  by  the  combustion  of  a  portion  of  the  wood;  by 
another  method,  the  material  to  be  charred  is  placed  in  a 
closed  retort  and  heat  is  applied  to  the  outside  of  this  retort. 

According  to  Peclet,  100  parts,  by  weight,  of  ordinary 
wood  containing  25  per  cent,  of  moisture  yields  17  to  22  parts 
of  charcoal  if  charred  in  a  heap,  or  28  to  30  parts  if  charred 
in  a  retort.  One-half  of  the  carbon  of  the  wood  is  burned 
in  making  charcoal  in  a  heap  and  one-fourth  in  charring  in 
retorts.  To  char  100  parts,  by  weight,  of  wood  in  a  retort, 
12i  parts  of  wood  must  be  burned  to  heat  the  retort,  hence, 
112i  parts  of  wood  are  required  to  produce  28  to  30  parts  of 
charcoal  in  a  retort. 

The  composition'  of  wood  charcoal  varies  greatly,  depend- 
ing on  the  temperature  at  which  the  wood  is  carbonized. 
Charcoal  made  from  black  alder  at  about  800°  F.  analyzed: 
carbon,  81.64  per  cent.;  hydrogen,  1.96  per  cent.;  oxygen 
and  nitrogen,  15.24  per  cent.;  ash,  1.16  per  cent.;  while 
that  made  from  the  same  wood  at  about  2,700°  F.  analyzed: 
carbon  94.57  per  cent.;  hydrogen,  .74  per  cent.;  oxygen  and 
nitrogen,  4.03  per  cent.;  ash,  .66  per  cent.  In  general,  the 
higher  the  temperature  at  which  the  carbonization  is  effected 
the  higher  will  be  the  percentage  of  carbon  and  ash  and  the 
lower  the  percentage  of  hydrogen,  oxygen,  and  nitrogen. 

23.  Uses  of  Charcoal. — Charcoal  was  at  one  time  the 
principal  fuel  used  for  smelting  iron  in  blast  furnaces.     It  is 


12  FUELS  §16 

still  used  to  a  small  extent  for  producing  a  very  fine  quality 
of  pig  iron,  but  most  furnaces  now  use  coke. 

In  some  localities,  charcoal  is  still  used  to  some  extent  as 
a  domestic  fuel.  It  is  also  largely  used  in  the  manufacture 
of  black  powders  (gunpowder  and  blasting  powder).  Owing 
to  its  power  to  absorb  gases  and  coloring  matters,  it  is  fre- 
quently used  in  filters  to  purify  water.  Charcoal  also  finds 
some  use  in  medicine. 

EXAMPLE. — One  hundred  pounds  of  wood  contains  39  pounds  of 
carbon,  1  pound  of  ash,  60  pounds  of  oxygen  and  hydrogen  in  propor- 
tion to  form  water;  one-third  of  the  carbon  is  burned  away  in  making 
charcoal.  How  many  pounds  of  charcoal  will  be  made,  and  what  per- 
centage of  ash  will  it  contain? 

SOLUTION.— Two-thirds  of  39  =  26  Ib.  of  carbon  to  which  is  added 
1  Ib.  of  ash  =  27  Ib.  charcoal.  Ans. 

1  X  100 

— == —  =  3.7  per  cent.  ash.     Ans. 


PEAT  OK  TURF 

24.  Peat  is  a  fuel  that  is  produced  in  nature  by  the 
accumulation    of    partly   decomposed   water    plants,    ferns, 
mosses,  and  other  vegetable  material.     It  is  found  all  over 
the  world  in  locations   such  as  bogs  or  marshes,  that  are 
favorable  to  the  growth  of  vegetation  and  to  the  retention  of 
the  decaying  products.     Recent  peat  shows  the  structure  of 
the  roots  and  stems  of  the  plants  from  which  it  is  formed. 
In  older  peat,  the  fibrous  organic  structure  has  given  place 
to  an  earthy  structure  more  or  less  dense.     The  freshly  cut 
surface  of  denser  varieties  appears  smooth  and  shining  like 
wax  or  pitch. 

25.  Composition. — Freshly   cut  peat   may  contain   as 
much  as  80  per  cent,  of  moisture;  air-dried  peat  usually  con- 
tains from  25  to  30  per  cent,  of  moisture.     The  moisture 
may  be  expelled  by  heating  the  peat  to  250°  F.  or  upwards, 
but  it  will  reabsorb  from  10  to  20  per  cent,  if  exposed  to  air. 

The  composition  of  entirely  dry  peat  of  the  best  quality 
is  given  by  Regnault  as  carbon,  58  per  cent.;  hydrogen, 
6  per  cent.;  oxygen,  31  per  cent.;  ash,  5  per  cent.  Peat 


§16 


FUELS 


13 


from  Oswego,  N.  Y.,  gave  the  following  composition: 
carbon,  44.11  per  cent.;  hydrogen,  6.14  per  cent.;  oxygen, 
33.39  per  cent.;  nitrogen,  .79  per  cent.;  ash,  15.57  per  cent. 
A  proximate  analysis  of  peat  from  Dismal  Swamp,  Va.,  is 
fixed  carbon,  24.52  per  cent.;  volatile  matter,  52.31  per  cent.; 
water,  20.22  per  cent.;  ash,  9.25  per  cent.  One  pound  of  air- 
dried  peat  will  evaporate  about  5i  pounds  of  water. 

The  quantity  of  ash  in  peat  depends  on  the  ash  in  the 
plants  from  which  it  is  derived  and  also  on  the  earthy 
matter  that  collects  in  the  bog  in  which  it  is  deposited. 
The  ash  in  many  samples  of  peat  from  different  parts  of 
Europe  has  been  found  to  range  from  1  to  33  per  cent. 

26.  Peat   may   be    compressed   by    machinery  to    from 
one-half  to  one-third  its  original  volume,  losing  much  of  its 
water  in  the  operation;  it  is  thus  made  denser  than  wood. 
Such  compressed  peat  will  prove  a  highly  valuable  fuel  in 
districts  remote  from  coal  mines  or  gas  wells,  where  wood 
is  expensive.  

COAL 

27.  Origin  of  Coal. — Coal  is  of  vegetable  origin  and 
the  manner  of  its  formation  has  been  fully  described  in  Geology 
of  Coal.     The  progressive  change  in  the  chemical  composition 
that  takes  place  when  woody  fiber  is  changed  to  coal  is  shown 
in  Table  III. 

TABLE  III 

CHANGES    IN    CHEMICAL,    COMPOSITION    FROM    WOOD 
TO    ANTHRACITE 


Substance 

Carbon 
Per  Cent. 

Hydrogen 
Per  Cent. 

Oxygen 
Per  Cent. 

Woody  fiber 

52  65 

5  25 

42  10 

Peat  from  Vulcaire  

59-57 

5.96 

34-47 

Lignite  from  Cologne     

66.04 

S-*7 

28.69 

Earthy  brown  coal  

73-18 

5-58 

21.14 

Coal  from  Belestat,  secondary    

75.06 

5.84 

19.10 

Coal  from  Rive  de  Gier     

89.29 

5-05 

5-66 

Anthracite,  Mayenne,  transition  formation 

91.58 

3-96 

4.46 

11 


FUELS 


§16 


CLASSIFICATION    OF    COALS 

28.  Coals  may  be  classified  from  different  standpoints 
depending  on  their  compositions,  their  behavior  on  the 
grate,  or  the  use  to  which  the  coal  is  put.  The  most  con- 
venient and  common  classification  is  one  based  on  the  com- 
position as  given  by  the  relative  percentages  of  fixed  carbon 

TABLE  IV 


Fixed 

Volatile 

Total 

Kind  of  Coal 

Carbon 

Matter 

Combustible 

Per  Cent. 

Per  Cent. 

Per  Cent. 

Anthracite    

97.0  to  92.5 

3-0  to     7.5 

IOO 

Semianthracite 

92.5  to  87.5 

7.5  to  12.5 

IOO 

Semibituminous    

87.5    tO    75.  Q 

12.5  to  25.0 

IOO 

Bituminous,    Eastern    United 

States    

75.0  to  60.0 

25.0  to  40.0 

IOO 

Bituminous,    Western    United 

States    

65.0  to  50.0 

35.0  to  50.0 

IOO 

Lignite  or  brown  coal     

under  50 

over  50 

IOO 

and  volatile  matter  determined  by  a  proximate  analysis; 
such  a  classification,  in  terms  of  combustible  matter,  is 
shown  in  Table  IV. 

Anthracite  and  semianthracite  are  commonly  called  hard 
coal,  the  other  varieties  soft  coal. 

TABLE    V 


Locality 

Moisture 
Per  Cent. 

Volatile 
Matter 
PerCent. 

Fixed 
Carbon 
PerCent. 

Ash 
PerCent. 

Sulphur 
PerCent. 

Cannelsburg  County,  Ind. 

1.47 

49-08 

26.35 

23.10 

1.48 

Carter  County,  Ky.      .    .    . 

.60 

66.30 

28.30 

4.80 

1.32 

Johnson  County,  Ky.  .    .    . 

1.20 

49.20 

44.00 

5-00 

•85 

Johnson  County,  Ky.  .    .    . 

1.  80 

64.39 

26.36 

8.05 

I.67 

Kanawha  County,  W.  Va. 

58.00 

23-50 

18.50 

29.     Cannel   coal   is   a  peculiar  variety   of   bituminous 
coal  distinguished  by  being  high  in  hydrogen.     It  is  used 


16 


FUELS 


15 


as  an  cnricher  in  gas  making,  on  account  of  the  illuminating 
quality  of  its  volatile  matter,  and  is  highly  valued  as  a  fuel 
for  open  fireplaces.  In  the  United  States  it  is  found  only  to 
a  limited  extent,  chiefly  in  Virginia,  West  Virginia,  Ten- 
nessee, and  Kentucky. 

Table  V  gives  the  proximate  analyses  of  some  American 
cannel  coals. 

Table  VI   gives  the  ultimate  analyses  of   some  foreign 
cannel  coals. 

TABLE    VI 

ULTIMATE  ANALYSES  OF  SOME  FOREIGN  CANNEL  COALS 


Locality 

C 

H 

0+N 

S 

Ash 

Boghead,  Scotland  .... 

63.10 

8.91 

7-25 

.96 

19.78 

Albertite,  Nova  Scotia    .    . 

82.67 

9.14 

8.19 

Tasmanite,  Tasmania     .    . 

79-34 

10.41 

4-93 

5-32 

30.  Caking  and  Non-Caking  Coal. — Bituminous  coals 
are  sometimes  classified  as  caking  or  non-caking,  according 
to  their  behavior  when  heated  to  a  temperature  approaching 
red  heat.    Caking,  or  coking,  coals,  when  thrown  into  a 
hot  fire  or  heated  in  an  oven,  partially  melt  and  run  together, 
forming  a  cake  or  crust.     When  this  crust  is  heated  to  a  red' 
heat,  or  higher,  the  volatile  matter  distils  off,  leaving  a  com- 
pact but  porous  mass  called  coke.     Non-caking  coals  hold 
their  original  shape  when  highly  heated  and  do  not  form  a 
crust.     Chemical  analysis  does  not  explain  the  difference  in 
action  of  the  two  kinds  of  coals,  for  a  caking  and  non-caking 
coal  may  have  the  same  chemical  composition.    This  subject 
is  fully  treated  in  Principles  of  Coking. 

31.  Long-Flaming   and    Short-Flaming   Coals. — A 

long-flaming  coal  is  one  that  has  a  high  percentage  of 
volatile  matter  "and  gives  off  a  long  flame  when  burned 
in  an  ordinary  furnace.  The  long  flame,  however,  is 
evidence  that  the  combustion  is  incomplete  in  the  furnace, 
rather  than  an  indication  of  the  quality  of  the  coal  itself,  for 
a  coal  that  in  one  furnace  bums  with  a  long  flame,  may  in 


16  FUELS  §  16 

another  furnace,  in  which  there  is  a  sufficient  supply  of  very 
hot  air,  be  made  to  burn  with  a  short  flame. 

32.  A  free-burning  coal  is  one  that  burns  easily  with 
a  light  draft.     This  term   is,   however,   often   used   rather 
indefinitely,  and  some  use  it  synonymously  with  non-caking, 
while  others  apply  it  to  a  coal  containing  a  larger  amount  of 
volatile  matter. 

33.  Coals  are  also  classified  in  accordance  with  the  use 
to  which  they  are  put,  as  steam  coal,  gas  coal,  domestic  coal, 
blacksmith  coal,  sea  coal,  etc. 

34.  Steam  Coals. — For  steam  making,  the  superiority 
of  coals  high  in  combustible  constituents  is  admitted,  and 
those  containing  from  75  to  90  per  cent,  of  fixed  carbon, 
with  25  to  10  per  cent,  of  volatile  matter,  in  the  combustible 
are  the  most  desirable.     Of  coals  high  in  fixed  carbon,  the 
semianthracites  and  the  semibituminous  rank  higher  than 
the  anthracites   in  meeting  the  various  requirements  of  a 
quick  and  efficient  steaming  coal. 

•  In  semibituminous  coals  the  comparative  absence  of 
smoke,  which  means  loss  of  combustible  matter,  is  sufficient 
to  suggest  their  superiority  over  bituminous  coals  for  steam 
raising.  Semibituminous  coals  are  specially  well  suited  for 
small  tubular  boilers,  firebox  steam  boilers,  or  other  forms 
with  small  unlined  combustion  chambers,  in  which  the  gases 
from  bituminous  coals  become  cooled,  are  not  burnt,  and 
deposit  soot  in  the  tubes.  The  high  rate  of  combustion  and 
the  strong  draft  necessary  in  locomotives  is  particularly 
unfavorable  to  the  economical  combustion  of  bituminous  coal. 

Steaming  coal  should  kindle  readily  and  burn  quickly  but 
steadily,  and  should  contain  only  enough  volatile  matter  to 
insure  rapid  combustion.  It  should  be  low  in  ash  and 
sulphur,  should  not  clinker,  and  when  it  is  to  be  transported 
should  not  easily  crumble  and  break. 

The  consideration  of  the  steaming  qualities  of  a  coal 
involves,  also,  a  consideration  of  the  form  of  furnace  and  of 
all  the  conditions  of  combustion.  The  evaporative  power  of 
a  coal  in  practice  cannot  be  stated  without  reference  to  the 


§  16  FUELS  17 

conditions  of  combustion,  and  every  practical  test  of  a  coal, 
to  be  thorough,  should  lead  to  a  determination  of  the  best 
form  of  furnace  for  that  coal,  and  should  furnish  knowledge 
as  to  what  class  of  furnaces  in  actual  use  such  coal  is  specially 
adapted.  It  is  not  sufficient  that  in  comparative  tests  of  coals, 
the  same  conditions  should  exist  with  each,  but  there  should 
also  be  determined  the  best  conditions  for  each  coal. 

35.  Domestic  Coals. — In  domestic  use,  coal  is  burned 
in  open  grates  and  in  closed  stoves.     The  coal  that  sustains 
a  mild,  steady  combustion,  does  not  coke  nor  smoke,  and 
remains  ignited  at  a  low  temperature  with  a  comparatively 
feeble  draft,  is  the  best.     A  coal  burning  with  a  smoky  flame 
is  objectionable  as  producing  much  soot  and  dirt,  especially 
for   open    grates    or   cooking    purposes.     For    self-feeding 
stoves,  a  dry,  non-caking  coal  is  necessary.     A  very  free 
and  fiercely  burning  coal  is  not   desirable,  particularly  in 
stoves,   as  the  temperature  cannot  be  easily  regulated.     A 
sulphurous  coal  is  also  bad,  as  it  gives  off  stifling  gases 
when  burning,  and  corrodes  the  grates  and  fire-pots.     Clink- 
ering   is  not  so    serious  a  matter  in  domestic  use  as  it  is 
under  boilers,  as  the  temperature  is  not  generally  high  enough 
to  fuse  the  ash.     A  stony,  hard  ash  that  will  not  pass  between 
the  grate  bars  is  bad,  and  light,  pulverulent  ash  is  best. 

36.  Gas  Coals. — Good  gas  coal  should  not  contain  more 
than  5  per  cent,  ash,  and  H  per  cent,  sulphur,  and  it  should  con- 
tain 30  to  40  per  cent,  of  volatile  hydrocarbons.     It  should 
yield  from  10,000  to  11,000  cubic  feet  of  gas  per  ton  of  coal. 
It  should  be  sufficiently  dense  to  bear  transportation  well,  so 
that,  when  carried  long  distances,  it  will  not  arrive  at  its 
destination  largely  reduced  to  slack  or  fine  coal;   it  should 
possess  coking  qualities  that  will  bring  from  the   retorts, 
after  carbonization,  about  60  per  cent,  of  coke. 

37.  Blacksmith  Coals. — A  good  coal  for  blacksmith 
purposes  should  have  a  high  heating  power,  should  contain 
but  a  small  amount  of  sulphur,  if    any,  should  coke    suffi- 
ciently to  form  an  arch  on  the  forge,  and  should  also  be  low 
in  ash. 


18  FUELS  §  16 

38.  Sea  coal  is  a  name  that  still  persists  in  iron  foun- 
dries. It  is  given  to  the  bituminous  coal  that  is  ground 
fine  and  used  for  facing  the  molds.  The  name  originated  in 
England,  where  coal  brought  by  sea  from  Newcastle  was 
called  sea  coal.  Pulverized  anthracite,  coke,  and  graphite 
are  used  for  the  same  purpose,  but  are  called  facings. 


COMPOSITION    OF    COAL 

39.  Moisture. — The  moisture  in  coal  consists  of  two 
portions,  first,  surface  moisture,  or  that  which  is  on  the 
exterior  surface  of  each  lump,  and  which  may  be  dried  off  in 
ordinary  dry  air;   second,  the  hygroscopic  moisture,   or 
that  which  is  held  by  capillary  attraction  in  the  pores  of  the 
coal  and  can  only  be  driven  out  of  a  lump  of  coal  by  heating 
it  considerably  above  212°  F.     The  percentage  of  surface 
moisture  that  may  be  held  in  a  pile  of  coal  depends  on  the 
size  of  the  pieces,  the  smaller  the  coal,  the  greater  is  the 
amount    of   moisture    that   it   will   hold.     Thus,   buckwheat 
anthracite,  or  slack  bituminous  coal,  after  exposure  to  rain, 
may  hold  as  much  as  8  or  10  per  cent. 

The  amount  of  hygroscopic  moisture  depends  on  the  kind 
of  coal;  thus,  anthracite  contains  practically  none,  or  less 
than  1  per  cent.;  semibituminous  coal  rarely  over  1  per  cent.; 
bituminous  coal  from  Pennsylvania,  between  1  and  2  per 
cent.;  from  Ohio,  about  4  per  cent.;  from  Illinois,  8  to  14 
per  cent.;  while  lignite  may  contain  20  per  cent,  or  more. 
A  sample  of  Illinois  coal  originally  containing  14  per  cent,  of 
moisture,  and  thoroughly  dried  by  heating  to  from  240°  F. 
to  280°  F.,  reabsorbed  the  same  amount  of  moisture  when 
exposed  to  ordinary  air  for  2  months. 

40.  Ash     in    Coal. — The     composition     of    coal     ash 
approximates   that  of  fireclay,    with   the   addition   of  ferric 
oxide,  sulphate  of  lime,  magnesia,  potash,  and  phosphoric 
acid. 

White-ash  coals  are  generally  freer  from  sulphur  than  red- 
ash  coals,  which  contain  iron  pyrites,  but  there  are  exceptions 
to  this  rule,  as  in  a  Peruvian  coal,  which  contains  more  than 


§16 


FUELS 


19 


10  per  cent,  of  sulphur  and  yields  not  a  small  percentage  of 
white  ash. 

The  fusibility  of  ash  varies  according  to  its  composition. 
It  is  the  more  infusible  the  more  nearly  its  composition 
approaches  fireclay,  or  silicate  of  alumina,  and  becomes 
more  fusible  with  the  addition  of  other  substances,  such  as 
iron,  lime,  etc.  Coals  high  in  sulphur  usually  give  a  very 
fusible  ash,  on  account  of  the  iron  with  which  the  sulphur  is 
in  combination.  A  fusible  ash  tends  to  form  a  clinker  on 
the  grate  bars,  and  therefore  is  objectionable. 

The  quantity  of  ash  in  different  coals  as  they  are  sent  to 
market  differs  greatly  according  to  the  quality  of  the  coal 
itself  and  the  care  taken  to  remove  the  slate,  dirt,  etc.  that 
accompany  them  as  they  come  from  the  mine.  A  lump  of 
coal  may  contain  only  5  per  cent,  of  ash,  while  the  average 
of  the  coal,  including  slate  and  dirt  as  it  is  mined,  may  con- 
tain 15  per  cent.  A  considerable  part  of  the  slate  may  be 
removed  from  the  larger  sizes  by  picking  after  screening, 
and  from  the  smaller  sizes  by  washing.  Usually  the  ash  in 
marketable  coal  is  higher  in  the  smaller  sizes,  as  shown  in 
Table  VII,  which  gives  analyses  of  anthracite  made  in  1901. 

TABLE  VII 


Size  of  Coal 

Fixed 
Carbon 
Per  Cent. 

Volatile 
Matter 
Per  Cent. 

Water 
Per  Cent. 

Ash 
Per  Cent. 

Broken    .... 
Egg     

88.300 
88.300 

5-750 
5.750 

.800 
.800 

5.150 
5.  l^O 

Stove  

88.650 

5.150 

.950 

5.250 

Nut      
Pea  

Buckwheat     .    . 
Rice     

87.325 
86.925 

85.725 
83.900 

5.650 
6.315 
6.160 
6.585 

.825 
•935 
.840 
•  765 

6.  200 
5.825 
7-275 

8.7CO 

Bird's  eye  .    .    . 

85-775 

6.500 

.700 

9.025 

41.     The  purest  varieties  of  semibituminous  and  bitumi- 
nous   coals    often  contain  less  than  2  per  cent,  of   ash  in 


TABL.E   VIII 

PROXIMATE    ANALYSIS    AND    HEATING    VALUE    OF 
AMERICAN    COALS 


Locality  and  Kind  of  Coal 

1 

Volatile  Matter 

Fixed  Carbon 

J3 

Sulphur 

Heating  Value 
per  Pound  of  Coal 
B.  T.  U. 

Fixed  Carbon,  Per  Cent,  of 
Combustible.  (Sulphur  Not  In- 
cluded as  Combustible) 

Anthracite 
Northern  coal  field 

3-65 
3-89 
3-40 
3-33 

1.56 
2.90 

1.48 
•75 
4.02 

1.59 
1.56 
1.94 
3.08 
1-73 
1.50 
1.05 

1.86 
1.63 
3-37 
1.96 
3-31 
3-93 
2.38 
3-83 
4.80 
7.84 

4.38 
3-08 
3-72 
4.28 
5-00 
5-93 
3-i8 

8.10 
9.40 
10.84 

15.61 
22.52 
19.20 
16.42 
I7-30 

21.00 

17-88 

30.12 
36.50 
35-90 
32-53 

35-33 
35-90 
35-04 
32.07 
34-60 
34-97 

83.27 
86.40 
81-59 
83.81 
81.00 
88.76 
88.71 

83-34 
83-69 
76.12 

77-30 
71.82 
71.12 
7I.5I 
73-12 
74-39 
77.64 

59.61 
59-05 
52.21 
60.99 
53-70 
50.19 
56.03 
57.60 
56.30 
48.85 

8.70 
6.63 
11.29 
8.58 
I4.OO 

3-75 

5-21 

7-08 
6.16 

8-35 

5-50 
4.10 
7-74 
8.99 

7-85 
3-" 
3-43 

8.41 
2.82 

8.02 

4-52 
7.66 
9.98 
6-55 
6.50 
4.30 
8-34 

•73 
•58 
•50 
.64 

.48 

1.63 
.91 
9.02 

.90 
.91 
1.70 
1.87 
•  74 
•  58 
•27 

.78 
.81 
i.  80 

I.OO 

1.98 
2.89 
1.28 

i-59 

13,160 
13,420 
12,840 
13,220 

13,920 
13,700 

14,870 
M,950 
14,450 
I4,2OO 
14,400 
15,070 
15,220 

14,050 
14,450 
13,410 
14,370 
13,200 
13,170 
14,040 
13,090 
13,010 
12,130 

95-00 
96.56 
95.64 
95-15 
94.19 
93-74 
96.54 

91.14 

89.90 
87.53 

83.19 
76.12 
78.74 
80.53 
80.86 
77.98 
81.28 

66.43 
61.80 
59-25 
65.21 
60.31 
58.29 
61.52 
64.24 
61.93 
58.28 

East  Middle  coal  field    

West  Middle  coal  field  
Southern  coal  field     

Lykens  Valley    Pa 

Crested  Butte    Colo                      .    .    . 

Las  Cerillos,  N.  Mex  
Sentianthracite 
Loyalsock  Field  

Coal  Hill   Ark 

Semibituminous 
Broad  Top   Pa 

Clearfield  County    Pa.             .... 

Cambria  County,  Pa  

Somerset  County,  Pa  
Cumberland,  Md  

New  River   W   Va 

Bituminous  (Carboniferous) 
Connellsville    Pa.                          .    .    . 

Youghiogheny,  Pa.        

Pittsburg,  Pa  
Jefferson  County,  Pa  
Middle  Kittanning  Seam,  Pa.     ... 
Upper  Freeport  Seam,  Pa.  and  Ohio 
Thacker,  W.  Va  
Jackson  County,  Ohio  

Brier  Hill    Ohio 

Hocking  Valley,  Ohio  

TABL.E  VIII—  (Continued} 


h 

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Bituminous  (Carboniferous) 

Vanderpool,  Ky  

4.00 

34-10 

54.60' 

7.30 

12,770 

61.55 

Muhlenberg  County,  Ky  

5-58 

33.65 

55.50 

5.27 

•57 

13,060 

62.25 

Scott  County   Tenn.              

2.76 

35.76 

53.14 

8.34 

.80 

13,700 

59.77 

Jefferson  County   Ala 

3.O5 

34-44 

59.77 

2.74 

.42 

63.44 

Pratt  Seam   Ala 

1.  12 

32.  17 

63.37 

.04 

1 

66  -n 

Sewanee,  Tenn  

27.81 

61.52 

10.67 

.22 

*-"-'OJ 

68.87 

Big  Muddy    111         

7.5O 

30.70 

53.80 

8.00 

12,400 

63.67 

Streator    111 

12.  OO 

33.3° 

40.70 

14.00 

10,580 

55.00 

Polk  County,  Iowa     

7-05 

40.06 

43.17 

9.27 

4.25 

51-87 

Rose  Hill,  Iowa   

4  01 

41  .69 

43.01 

10.39 

5.OI 

50.78 

Brazil,  Ind.            .    .           

8.98 

34-44 

50.30 

6.28 

1-39 

59.36 

Osage   Kans 

7.19 

40.03 

41  .13 

11.65 

50.68 

Missouri      

6.44 

37-57 

47.94 

8.05 

56.06 

Bituminous  (Post  Carboniferous) 

Nanaimo,  Vancouver  Island  (Creta- 

ceous)       

1.70 

38.10 

48.48 

11.72 

55-99 

Trinidad,  Colo.  (Cretaceous)     .    .    . 

I.I5 

30.20 

58.04 

10.61 

•59 

65-75 

Carbonado,  Wash.  (Cretaceous)   .    . 

1.74 

30.70 

58.30 

9.26 

65-51 

Skagit  River,  Wash.  (Cretaceous)    . 

1-52 

18.68 

70.21 

9-59 

•95 

78.98 

Cook's  Inlet,  Alaska  (Cretaceous)    . 

9-31 

46.14 

40.85 

3-70 

46.96 

Great  Falls,  Mont.  (Cretaceous)    .    . 

5.86 

18.40 

64.33 

11.41 

•43 

77-77 

Rocky  Fork,  Mont.  (Cretaceous)  .    . 

8.  ii 

43-29 

46.56 

2.04 

51.82 

Rock  Springs,  Wyo.  (Cretaceous)    . 

7.00 

36.87 

54.40 

1-73 

59.60 

Richmond,  Va.  (Triassic)    

32.00 

59.25 

8.75 

64-93 

Lignites  and  Lignitic  Coals 

Wyoming       

8.19 

38.72 

41.83 

1  1.26 

10,390 

51.93 

Utah                              

10.39 

41  .97 

44-37 

3.27 

1.18 

11,030 

51  .40 

Oregon  Lignite    

16.55 

42.98 

33-32 

7-15 

1.66 

8,540 

Coos  Bay,  Ore  

15-45 

41-55 

34-95 

8.05 

2-53 

45-69 

Vogel  Mine,  Tex  

18.45 

37.85 

37.40 

6.30 

.80 

49.70 

Lytle  Lignite,  Tex  

14-45 

40.62 

36.47 

8.46 

1.26 

47-31 

Monte  Diablo,  Cal  

13.01 

42.  15 

34.23 

10.61 

44.81 

22 


FUELS 


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§  16  FUELS  23 

picked  samples,  and  less  than  5  per  cent,  as  marketed.  Any 
coal  with  less  than  10  per  cent,  is  usually  considered  to  be 
good,  marketable  coal.  Some  of  the  poorer  coals  run  much 
higher  than  10  per  cent,  of  ash  on  the  average,  some  varie- 
ties containing  30  per  cent,  or  more. 

42.  Table  VIII  gives  the  proximate  analysis  and  heating 
value  of  a  large  number  of  coals  from  the  different  fields  of 
the  United  States. 

43.  Table  IX  gives  the  ultimate  or  elementary  analyses 
of  a  number  of  coals.          

VALUATION  OF  COALS  AS  FUEL, 

44.  Relation  of  Heating  Value  of  Coal  to  Composi- 
tion of  Combustible. — The  volatile  combustible  matter  in 
coal  consists  of  carbon,  hydrogen,   and  oxygen  in  various 
proportions,  differing  with  the  character  of  the  coal.     It  is 
found  that,  with  the  exception  of  cannel  coal,  the  larger  the 
percentage  of  volatile  matter  in  a  coal,  the  greater,  usually, 
is  the  proportion  of  oxygen  in  the  volatile  matter.     It  also 
appears  that  in  the  semibituminous  coals,  after  deducting  as 
much  of  the  hydrogen  as  is  needed  to  form  water  with  the 
oxygen,   that  is,   one-eighth    as  much    as    the   oxygen,   the 
remainder,  or  the  available  hydrogen,  is  combined  with  car- 
bon in  about  the  proportion  forming  methane,  or  marsh  gas, 
C7/«,  or  three  parts,  by  weight,  of   carbon  to  one  part  of 
hydrogen;  while  in  the  bituminous  coals  it  is  combined  in 
about  the  proportions  of  five  parts,  by  weight,  of  carbon  to 
one  part  of  hydrogen.     The  low  heating  values  per  pound  of 
combustible,  in  coals,  which  are  high  in  volatile  matter  and 
in  oxygen,  are  thus  accounted  for.     According  to  William 
Kent,  a  relation  exists  between  the  amount  of  fixed  carbon 
in  the  combustible  portion  of  a  coal,  and  its  heating  value 
per  pound  of  combustible,  which  is  shown  in  Table  X. 

These  figures  are  correct  within  2  per  cent,  for  all  coals 
containing  more  than  63  per  cent,  of  fixed  carbon  in  the 
combustible,  but  for  coals  containing  less  than  60  per  cent, 
fixed  carbon  or  more  than  40  per  cent,  volatile  matter  in  the 


24 


FUELS 


§16 


combustible  they  are  liable  to  an  error,  in  either  direction, 
of  about  4  per  cent.  The  greater  variation  in  the  coals  low 
in  fixed  carbon  and  high  in  volatile  matter  is  due  to  the  fact 
that  they  differ  considerably  in  the  percentage  of  oxygen  in 
the  volatile  matter. 

TABLE  X 

APPROXIMATE  HEATING  VALUE  OF  COALS 


Fixed  Carbon  in  Coal 
Dry  and  Free  From 
Ash 
Per  Cent. 

Heating  Value  per  Pound 
Combustible 

B.  T.  U. 

Calories 

IOO 

14,580 

8,100 

97 

14,940 

8,300 

94 

15,210 

8,450 

90 

15,480 

8,600 

87 

I5,66o 

8,700 

80 

15,840 

8,800 

72 

I5,66o 

8,700 

68 

15,480 

8,600 

63 

15,120 

8,400 

60 

14,760 

8,200 

57 

14,220 

7,900 

55 

I3,86o 

7,700 

53 

13,320 

7,400 

5i 

12,420 

6,900 

EXAMPLE. — What  is  the  approximate  heating  value  of  a  coal  whose 
proximate  analysis  is:  moisture,  2  per  cent.;  volatile  matter,  18  per 
cent.;  fixed  carbon,  72  per  cent.;  ash,  8  per  cent.? 

SOLUTION.— Since  the  coal  contains  2  per  cent,  moisture  and  8  per 
cent,  ash,  the  amount  of  combustible  is  100  -  (2  +  8)  =90  per  cent. 
The  percentage  of  fixed  carbon  in  the  combustible,  that  is  to  say,  in 

80  per  cent.     By  Table  X, 


72  X  100 
the  coal  dry  and  free  from  ash,  is — 


the  approximate  heating  value  per  pound  of  combustible  for  a  coal 
dry  and  free  from  ash  and  containing  80  per  cent,  fixed  carbon  is 
15,840  B.  T.  U.,  and  since  the  coal  contains  90  per  cent,  combustible, 
15,840  X  .90  =  14,256  B.  T.  U.  per  Ib.  of  coal.  Ans. 


§16  FUELS  25 

45.  Practical  Values  of  Fuel  for   Different  Uses. 

The  total  heating  value  of  a  fuel,  as  determined  by  a  calorim- 
eter, would  be  a  correct  measure  of  its  practical  value  for 
use  in  the  industrial  arts  if  all  fuels  were  equally  convenient 
to  handle  and  all  could  be  used  with  the  same  efficiency; 
that  is,  if  the  same  proportion  of  their  total  heating  value 
could  be  utilized.  In  practice,  however,  it  is  found  that  of 
two  fuels  of  the  same  heating  value,  one  may  be  more  valu- 
able for  some  specific  use  than  another,  on  account  of  differ- 
ence in  its  physical  condition  or  in  the  conditions  under 
which  it  is  used.  For  example,  clean  anthracite  lump  may 
be  crushed  and  sorted  by  screens  into  different  sizes, 
ranging  from  broken  to  buckwheat,  and  if  equally  free  from 
slate,  all  the  sizes  may  have  the  same  heating  value  per 
pound,  yet  one  size  will  be  preferred  for  a  certain  use,  and 
a  different  size  for  another  use;  and  the  market  values  of 
the  several  sizes  may  vary  considerably,  according  to  the 
relative  supply  and  demand  of  each.  Again,  an  anthracite 
and  a  bituminous  coal  may  have  the  same  heating  value,  but 
the  anthracite  will  be  preferred  for  use  under  a  steam  boiler 
provided  with  an  ordinary  furnace,  for  the  reasons  that  a 
greater  percentage  of  the  heat  generated  may  be  utilized  in 
making  steam,  and  that  it  may  be  burned  without  smoke. 
So,  f  ton  of  coke  made  from  1  ton  of  bituminous  coal,  and 
having  less  than  two-thirds  of  the  heating  value  of  the  ton  of 
coal,  may  have  a  market  value  considerably  higher  than  the 
ton  of  coal,  on  account  of  its  being  better  suited  for  use  in  a 
blast  furnace,  or  the  cupola  of  an  iron  foundry.  Anthracite 
may  be  used  in  a  blast  furnace,  but  coke  of  the  same  heating 
value,  even  at  a  higher  price,  will  be  preferred,  on  account  of 
the  fact  that  with  coke  the  furnace  may  be  driven  much  faster. 
Coke  is  far  superior  to  bituminous  coal  for  a  blast  furnace, 
for  the  reason  that  the  volatile  matter  of  the  coal  is  all  driven 
off  in  the  upper  part  of  the  furnace,  where  it  is  of  no  use,  at 
the  expense  of  fuel  burned  at  the  bottom  of  the  furnace. 

46.  In  estimating  the  relative  practical  value  of  different 
fuels,  account  must  be  taken  not  only  of  the  cost  of  fuel 


FUELS 


§16 


having  a  certain  heating  value,  but  also  of  the  percentage  of 
the  total  heating  value  that  may  be  utilized.  The  cost  for 
storage,  insurance,  labor  in  handling  the  fuel,  and  the  ashes 
made  from  it,  must  also  be  considered,  as  well  as  the  first 
cost,  and  cost  of  maintenance  and  operation  of  apparatus 
required  for  handling  it;  such  as  automatic  stokers  for  coal, 
steam  jets  for  oil,  etc.  Regard  must  also  be  had  for  the 
capacity  of  the  furnace  for  burning  a  sufficient  quantity  of  the 
coal  to  produce  the  desired  result;  for  instance,  if  a  furnace 
boiler  and  chimney  are  designed  to  produce  a  given  maximum 
horsepower  from  semibituminous  coal  and  the  full  capacity  of 
the  boiler  is  required,  it  would  be  impossible  to  obtain  it  with 
anthracite  buckwheat  without  a  reconstruction  of  the  furnace 
or  the  Use  of  forced  draft.  It  may  also  be  necessary  to  change 
the  grate  bars  and  substitute  shaking  grates  for  plain  grates  in 
order  to  prevent  obstruction  of  the  draft  by  ashes  and  clinker. 

TABLE   XI 
HEATING    VALUE    OF    DIFFERENT    COALS 


Coals 

Average  Relative  Heating  Value  of  Different  Coals 

Mois- 
ture 
Per 
Cent. 

Ash 
Per 
Cent. 

Fixed 
Carbon  in 
Dry  Coal 
Free 
From  Ash 
Per  Cent. 

Heating  Values 

Relative  Values 
Semibitumi- 
nous -    100 

Per 
Pound 
Combus- 
tible 

Per 

Pound 
Coal 

Combus- 
tible 

Coal 

Anthracite     .... 

2 

12 

95 

14,700 

12,600 

93 

89 

Semianthracite     .    . 

2 

12 

90 

15,100 

13,000 

96 

92 

Semibituminous 

2 

8 

80 

15,750 

14,200 

IOO 

IOO 

Bituminous,  Eastern 

2 

8 

65 

15,000 

13,500 

95 

95 

Bituminous,  Western 

8 

15 

55 

14,200 

II,OOO 

90 

77 

Lignite    

15 

20 

45 

I2,2OO 

7,900 

77 

56 

47.     Relative    Practical    Values    of    Steam    Coals. 

Table  XI  shows,  approximately,  the  relative  total,  or  theo- 
retical heating  values  of  different  classes  of  coal.  Table  XII 
shows  their  relative  practical  values  for  steam-boiler  pur- 
poses, based  on  the  assumption  that  a  clean  boiler,  provided 
with  an  ordinary  form  of  furnace,  gives  the  several  specified 


16 


FUELS 


27 


percentages  of  efficiency  with  the  different  coals.  The  heat 
utilized  is  computed  by  multiplying  the  heating  value,  in 
B.  T.  U.,  by  the  boiler  efficiency. 

TABL.E  XII 

RELATIVE    PRACTICAL    VALUES    OF    COALS,    ASSUMING 
DIFFERENT    EFFICIENCIES    OF    BOILER 


Effi- 

Heating 

ciency 

Heat 

Relative 

' 

Value  per 

of 

Utilized  per 

Value 

Coals 

Pound  Coal 

Boiler 

Pound  Coal 

Semibitumi- 

B. T.  U. 

Per 

B.  T.  U. 

nous  =  100 

Cent. 

Anthracite      .... 

12,600 

77 

9,700 

91.1 

Semianthracite      .    . 

13,000 

76 

9,880 

92.8 

Semibituminous    .    . 

14,200 

75 

10,650 

IOO.O 

Bituminous,  Eastern 

13,500 

70 

9,450 

88.7 

Bituminous,  Western 

II,OOO 

65 

7,150 

67.1 

Lignite   

7,900 

60 

4,740 

44.5 

48.  In  Table  XII,  the  figures  in  the  column  headed 
Efficiency  of  Boiler  are  about  the  maximum  that  can  be 
obtained  with  ordinary  furnaces  and  with  the  most  skilful 
firing.  With  special  furnaces,  adapted  to  burn  all  the 
volatile  matter  distilled  from  the  coal,  the  efficiency  of  the 
boiler  may  be  brought  up  to  75  per  cent,  with  bituminous 
coals,  and  to  nearly  that  figure  with  lignites. 

The  figures  in  the  last  column  show  that  a  ton  of  lignite 
may  be  worth  to  the  user  only  44.5  per  cent,  as  much  as  a 
ton  of  semibituminous  coal.  It  really  may  be  worth  much 
less  than  this,  on  account  of  the  extra  labor  required  to 
handle  it,  and  of  the  trouble  given  by  the  ashes;  and  it  may 
even  be  worth  nothing  when  semibituminous  coal  is  pro- 
curable at  any  reasonable  price,  if  the  boiler  furnace  is  of 
restricted  size,  having  the  capacity  to  develop  the  rated 
power  with  the  good  coal  but  not  with  the  lignite. 

In  order  to  develop  the  rated  power  of  a  boiler  with 
poor  coal,  high  in  ash,  it  is  necessary  to  have  either  a  larger 


28  FUELS  §  16 

grate  surface  or  a  stronger  draft  than  with  good  coal.  Some- 
times a  strong  draft  is  of  no  avail,  on  account  of  clinkering 
of  the  ash,  in  which  case  a  large  grate  surface  is  absolutely 
required. 

EXAMPLE  1. — Assuming  that  a  coal  having  a  heating  capacity  of 
14,256  B.  T.  U.  is  burned  under  a  boiler  giving  an  efficiency  of  75  per 
cent.,  what  is  the  evaporation  from  and  at  212°  F.  if  it  takes  965.8 
B.  T.  U.  to  evaporate  1  pound  of  water  from  and  at  212°  F.? 

SOLUTION.—    14,256  X  .75  -^  965.8  =  11.07  Ib.  of  water.    Ans. 

EXAMPLE  2.— Suppose  that  this  coal  costs  $5  per  ton,  and  another 
coal  of  12,000  B.  T.  U.  heating  value  can  be  obtained,  giving  a  boiler 
efficiency  of  only  60  per  cent.;  what  is  the  value  of  this  other  coal? 

SOLUTION.—    }2'™  *  '%!  X  5  =  $3.367  per  ton.    Ans. 

14, ZOO  X  • ' 0 

49.  Valuing  Coals  by  Test  and  by  Analysis. — Coal 
is  usually  sold  by  the  name  of  the  mine  or  of  the  district  in 
which  the  mine  is  located,  without  any  other  guarantee  of 
its  quality.  For  the  purchaser's  interest,  it  should  be  sold 
on  a  guarantee  of  the  quality  as  determined  by  a  trial  test  or 
by  analysis. 

The  best  way  to  obtain  the  relative  value  of  different  coals 
for  any  particular  steam-boiler  plant  is  to  have  a  car  load  of 
each  coal  tested  under  the  ordinary  running  conditions  of  the 
plant,  and  then  to  check  the  results  by  a  proximate  analysis 
of  each.  The  coal  that  is  most  economical  for  one  boiler 
plant  is  not  necessarily  the  most  economical  for  another,  on 
account  of  the  differences  in  conditions,  such  as  kind  of 
furnace,  area  of  grate  surface,  draft  available,  etc.  A  plant 
designed  for  the  purpose  may  be  able  to  use,  with  satisfaction, 
the  poorest  quality  of  the  fine  sizes  of  anthracite,  while 
another  may  not  be  able  to  use  anything  cheaper  than  the 
best  pea  coal,  and  still  another,  having  deficient  grate 
surface,  may  be  compelled  to  use  egg  size,  or  even  semi- 
bituminous  coal. 

Furthermore,  it  is  equally  evident  that  no  comparison  of 
the  steaming  qualities  of  coals  can  be  made  when  burned 
under  different  types  of  boilers.  Not  only  must  the  boilers 
be  the  same,  but  also  all  other  conditions  (though  some  can 
be  allowed  for)  even  to  having  the  same  fireman.  A  test  is 


§16 


FUELS 


29 


of  value  in  showing  what  a  certain  coal  will  do  under  a 
certain  boiler,  and  if  some  other  coal  has  been  tested  under 
the  same  conditions  a  comparison  is  possible,  but  it  does 
not  prove  that  the  one  is  absolutely  the  best,  only  the  best 
under  that  particular  boiler.  It  can  be  imagined  that  were 
the  boilers  or  furnaces  changed  to  a  type  better  suited  to  the 
coal  making  a  poor  showing,  the  results  might  be  reversed. 
These  tests  are  usually  made  by  trained  engineers  and  the 
details  need  not  be  entered  into  here.  The  coal  is  fired  as 
usual,  but  the  amount  of  steam  generated  and  its  temperature 
are  noted,  the  temperature  of  the  escaping  gases  and  their 
composition  are  determined,  the  coal  is  weighed  before  firing 
and  the  ash  afterwards,  and  the  amount  and  temperature  of 
feedwater  entering  the  boiler  are  measured.  From  these 
and  other  data  the  efficiency  of  the  boiler  with  that  particular 
coal  is  determined. 

TABLE  XIII 


. 

2 

3 

Moisture,  per  cent. 

3OO 

82 

i  6* 

Volatile  matter,  per  cent  

19-15 

25.54 

32.08 

Fixed  carbon,  per  cent  

68.39 

64.70 

58.28 

Ash,  per  cent  

9.46 

9.2C 

8.01 

Sulphur  (separate  determination), 

per  cent.    .        .        .    . 

1.77 

1.77 

1.75 

Theoretical  B.  T.  U. 

12  203 

12  6'?'? 

11  O72 

Theoretical  evaporation  from  and 

at  212°  F.  (pounds  of  water)  .    . 

12.635 

13.101 

13-535 

Actual    evaporation    from   and    at 

212°  F.  (pounds  of  water)  .    .    . 

9.788 

9.990 

9.712 

Efficiency  of  boiler,  per  cent.  .    .    . 

77-4 

76.2 

71.7 

50.  Table  XIII  shows  the  results  obtained  with  three 
coals  under  the  same  boiler.  The  theoretical  B.  T.  U.  were 
calculated  from  the  analyses,  from  which  the  theoretical 
evaporating  powers,  that  is,  pounds  of  water  evaporated 
from  and  at  212°  F.  per  pound  of  coal,  were  determined  by 


30  FUELS  §  16 

dividing  by  965.8,  the  number  of  B.  T.  U.  required  to  change 
1  pound  of  water  at  212°  F.  into  steam  at  212°  F. 

It  will  be  noted  that  these  coals,  in  the  order  of  theoretical 
evaporation,  are  3,  2,  1  and  in  actual  results,  2,  1,  3.  This 
was  natural,  as  the  boiler  used  was  one  designed  for  burning 
short-flamed  anthracite.  The  shortest  flame  semibituminous 
coal,  No.  1,  though  the  poorest  of  the  three,  in  theoretical 
heating  value  gave  the  highest  boiler  efficiency.  This  was 
probably  due  to  the  fact  that  this  coal  was  more  completely 
burned  in  the  furnace,  on  account  of  its  having  the  lowest 
percentage  of  volatile  matter. 

51.  The  value  of  such  tests  is  apparent,  although  usually 
but  little  understood  or  appreciated  by  consumers  of  coal. 
A  pure  coal  at  a  high  price  is  frequently  cheaper  in  the  end 
than  an  inferior  fuel  at  much  less  cost.     A  saving  is  effected 
in  every  way;  there  is  less  coal  required  to  do  the  same  work 
and  consequently  less  labor  to  pay  for  handling;  fewer  ashes 
to  cart  off,  hence  less  cost  of  teaming.     Not  having  to  renew 
grate  bars  destroyed  by  clinker  is  a  further  pecuniary  gain. 

52.  Selling   Coal   by  Analysis. — Besides  testing  the 
coals  by  burning  them  under  the  boilers  and  weighing  the 
quantity  of  water  evaporated,  a  proximate  analysis  of  each 
coal  should  be  made  so  as  to  arrive  at  a  standard  of  quality, 
by  reference  to  which  future  purchases  may  be  made.     A 
schedule  of  relative  values  may  then  be  prepared,  something 
like  the  following: 

Anthracite  and  Semianthracite. — The  standard  is  a  coal  con- 
taining 5  per  cent,  volatile  matter,  not  over  2  per  cent,  mois- 
ture, and  not  over  10  per  cent.  ash.  A  premium  of  1  per 
cent,  on  the  price  will  be  given  for  each  per  cent,  of  volatile 
matter  above  5  per  cent,  up  to  and  including  15  per  cent, 
and  a  reduction  of  2  per  cent,  on  the  price  will  be  made  for 
each  1  per  cent,  of  moisture  and  ash  above  the  standard. 

Semibituminous  and  Bituminous. — The  standard  is  a  semi- 
bituminous  coal  containing  not  over  20  per  cent,  volatile 
matter,  2  per  cent,  moisture,  6  per  cent.  ash.  A  reduction 
of  1  per  cent,  in  the  price  will  be  made  for  each  1  per  cent,  of 


§  16  FUELS  31 

volatile  matter  in  excess  of  25  per  cent.,  and  of  2  per  cent,  for 
each  1  per  cent,  of  ash  and  moisture  in  excess  of  the  standard. 

EXAMPLE. — If  the  standard  semibituminous  coal  is  worth  $5  per  ton, 
what  should  be  the  market  value  of  a  coal  containing  40  per  cent,  of 
volatile  matter,  8  per  cent,  of  moisture,  and  16  per  cent,  of  ash? 

SOLUTION. — The  excess  of  volatile  matter  is  40  —  20  =  20  per  cent.; 
of  moisture,  8  —  2  =  6  per  cent.;  of  ash,  16  -  6  =  10  per  cent.  The 
deductions  on  account  of  these  excesses  are: 

PER  CENT. 

,   For  volatile  matter,  20  X  1 20 

For  moisture,  6X2      12 

For  ash,  10  X  2      20 

Total 5~2 

The  value  of  the  coal  is  100  -  52  =  48  per  cent,  of  $5;  $5  X  .48 
=  $2.40  per  ton.  Ans. 

53.  Market  Value  of  Coal. — The  items  that  enter  into 
the  making  of  the  market  price  of  coal  are  the  following: 
Cost  of  the  coal  in  the  ground,  or  royalty  to  the  owner;  cost 
of  mining,  crushing,  screening,  picking,  washing,  etc.  at  the 
mine,  including  repairs,  interest  on  investment,  and  profit  to 
the  mine  operator;   freight  rates;    cost  of    selling,   storage, 
insurance,  distribution    to  the  final  consumer,  agents'  'and 
retail  dealers'  profits,  etc.;   relative  demand  and  supply  of 
the  different  qualities  and  sizes;  prejudice  in  favor  of  a  coal 
of  a  particular  name;  etc. 

54.  Weathering    of    Coal. — It  is  commonly  believed 
that   coal  when    exposed   to   the  weather   for  a  long  time 
loses  much  of  its  heating  value.     Careful  experiments  show 
that  the  loss  is  usually  very  slight.     The  only  change  that 
takes  place  in  anthracite  on  exposure  to  weather  is  the  oxida- 
tion of  such  iron  pyrites  as  it  may  contain  to  iron  sulphate. 
As  this  salt  is  soluble  and  may  be  washed  away,  the  change 
is  rather  of  advantage  than  otherwise.    Analyses  and  calorific 
determinations  of  unweathered  and  weathered  samples  of  sev- 
eral bituminous  and  semibituminous  coals,  the  latter  exposed 
to  the  weather  for  11  months,  showed  an  average  decrease 
of  heating  value  of  about  2  per  cent.,  as  calculated  from  the 
analyses,  but  only  one-half  of  1  per  cent,  as  determined  by 
the  calorimeter.     A  sample  of  Pocahontas  coal  exposed  in  a 


32  FUELS  §  16 

coal  yard  3  years,  showed  a  heating  value  per  pound  of  com- 
bustible as  calculated  from  the  analysis,  of  16,113  B.  T.  U. 
per  pound.  This  is  a  very  high  figure,  considerably  above 
the  average  for  freshly  mined  Pocahontas  coal. 

55.  Such  effect  as  weathering  may  have  seems  to  be  due 
to  the  oxidation  of  a  part  of  the  disposable  hydrogen  of  the 
coal,  increasing  the  percentage  of  oxygen,  but  the  effect  is 
usually  slight. 

Richters  found  that  at  a  temperature  of  158°  to  180°  F., 
three  coals  lost  in  14  days  an  average  of  3.6  per  cent,  of 
calorific  power. 

It  appears  from  the  experiments  of  Richters  and  Reder 
that  when  there  is  no  rise  in  the  temperature  of  coal  piled  in 
heaps  and  left  exposed  to  the  air  during  9  to  12  months,  it 
undergoes  no  sensible  change  in  any  respect;  and  that,  on 
the  other  hand,  when  the  coal  becomes  heated,  it  suffers 
precisely  the  same  kind  of  change  that  was  found  by  Richters 
to  be  effected  in  coal  by  heating  it  in  contact  with  atmos- 
pheric air  to  a  comparatively  low  temperature;  namely,  an 
increase  in  the  absolute  weight  of  the  coal  owing  to  the 
oxidation  of  some  of  the  carbon  and  hydrogen. 

56.  The  foregoing  statements  refer  more  particularly  to 
the  theoretical  heating  values  of   coals.     Certain  coals,  on 
exposure  to  the  weather,   slack  or  break   into  fine  pieces 
or  even  dust,  in  which  form  they  cannot  be  transported  or 
burned  by  the  ordinary  methods.     Hence,  while  the  theo- 
retical calorific  power  of  such  coals  may  remain  practically 
unchanged  by  weathering,  the  value  of   the  coal   may  be 
impaired  by  exposure   to    the    air.     Some    semibituminous 
coals,  however,  give  as  good  results  when  they  are  largely 
reduced  to  dust  by  weather  and  handling  as  when  they  are 
in  lumps.  

SPONTANEOUS    IGNITION    OF    COAL, 

57.  Coal  kept  in  storage,  either  in  stock  piles  or  in  the 
coal  bunkers  on  steamships,  etc.,  may,  under  certain  condi- 
tions, take  fire  spontaneously.     This  is  particularly  true  of 


§  16  FUELS  33 

bituminous  coals,  but  it  seldom  occurs  with  anthracite,  except 
in  the  case  of  culm  banks.  The  cause  of  the  spontaneous 
ignition  of  coal  was  formerly  thought  to  be  the  oxidation  of 
pyrites  contained  in  it;  it  has  been  learned,  however,  that  this 
is  not  the  principal  cause,  although  in  the  presence  of  air  and 
moisture  the  oxidation  of  pyrites,  if  present  in  sufficient 
quantity,  may  aid  in  the  generation  of  heat.  Coal  naturally 
absorbs  oxygen  from  the  air  and  in  so  doing  generates  heat, 
undergoing  a  process  of  slow  combustion.  The  temperature 
attained  depends  on  the  rapidity  of  the  absorption  of  the 
oxygen  and  the  rate  at  which  the  heat  generated  escapes. 
The  absorption  of  oxygen  is  greatly  influenced  by  the  degree 
of  fineness  of  the  coal  and  the  temperature  of  the  interior  of 
the  pile;  and  the  latter  by  the  size  of  the  heap  and  the  ventila- 
tion of  its  interior.  The  finer  the  coal  the  greater  is  the 
surface  exposed  to  the  action  of  the  air,  and  the  absorption 
of  oxygen  becomes  more  energetic  as  the  temperature  is 
increased;  hence,  it  is  evident  that  the  cooler  the  heap  can  be 
kept  and  the  freer  from  fine  coal,  the  less  will  be  the  danger  of 
spontaneous  ignition.  Large  heaps  hold  the  heat  better  than 
small  ones,  and  are  not  as  readily  ventilated.  While  good  ven- 
tilation cools  the  heap,  very  poor  ventilation  may  not  allow 
sufficient  oxygen  to  enter  the  pile  to  cause  spontaneous  com- 
bustion; therefore,  the  greatest  danger  lies  midway  between 
the  two  conditions.  Although  the  amount  of  heat  produced 
by  the  oxidation  of  the  pyrites  in  the  coal  is  small,  this 
oxidation  breaks  up  the  coal  and  thus  presents  fresh  surfaces 
for  the  absorption  of  oxygen.  The  greatest  occurrence  of 
spontaneous  combustion  of  coal  is  on  steamships,  where  the 
coal  bunkers  become  heated  owing  to  their  poor  ventilation. 

58.  The  subject  of  the  spontaneous  ignition  of  coal  was 
investigated,  in  1899,  by  a  board  appointed  by  the  Secretary 
of  the  United  States  Navy.  The  following  excerpts  taken 
from  the  report  of  this  board  are  of  interest.  While  the 
condensation  and  absorption  of  oxygen  is  always  going  on 
to  a  limited  extent,  the  general  immunity  of  bunker  coal  in 
the  Navy  from  spontaneous  ignition  shows  that  where  fire 


34  FUELS  §  16 

results  there  is  probably  a  further  exciting  cause  producing 
the  ignition  of  the  coal,  and  this  is  generally  thought  to  be 
due  chiefly  to  external  heat. 

Spontaneous  ignition  is  of  infrequent  occurrence,  and  the 
total  number  of  fires  due  to  this  cause  in  the  United  States 
Navy  in  3i  years,  counting  fire  in  each  bunker  as  a  separate 
fire,  was  only  twenty  that  occurred  on  ten  ships;  arid  when 
we  reflect  that  during  that  time  there  have  been  at  least 
forty  ships  in  commission  averaging  probably  forty  bunkers 
each,  and  that  these  have  probably  coaled  an  average  of 
twenty  times,  the  percentage  of  bunker  fires  is  seen  to  be 
very  low.  Diligent  inquiry  has  not  developed  a  single 
instance  of  spontaneous  ignition  of  anthracite  in  such  sizes 
as  come  on  board  ship.  With  bituminous  coal,  lumps  of 
large  size  and  as  free  as  possible  from  small  coal  and  slack 
should  be  preferred;  and  if  practicable,  the  coal  should  be 
screened  before  taking  on  board. 

Whenever  possible,  coal  with  a  low  percentage  of  com- 
bustible volatile  matter  and  little  or  no  pyrites  should  be 
used  on  board  ship  and  in  like  places.  In  any  case,  coals  of 
established  reputation  should  be  chosen,  even  at  a  higher 
price.  Such  coal  is  generally  freer  from  slack  and  pyrites 
than  another  coal,  and  not  only  less  liable  to  spontaneous 
ignition,  but  is  cheaper  in  the  end. 

With  respect  to  moisture,  it  is  always  preferable  to  take 
coal  on  board  dry;  but  when  wet  coal  must  be  taken  it  should 
be  used  first,  if  practicable,  and  the  bunkers  into  which  it  is 
put  examined  at  regular  intervals.  In  general,  recently 
mined  coal  should  not  be  taken,  as  the  fresh  coal  is  more 
greedy  of  oxygen  than  after  the  absorbing  process  has  pro- 
ceeded for  some  time.  The  coal  should  be  mined  at  least  a 
month  previous  to  being  stored. 

59.  With  respect  to  the  temperature  likely  to  cause  igni- 
tion, Professor  Lewes  states:  "If  the  bunker  coal  next  the 
bulkhead  be  kept  at  120°  F.,  any  coal  having  a  tendency  to 
absorb  oxygen  will  run  a  great  chance  of  igniting  within  a 
few  days." 


§  16  FUELS  35 

60.  Fires  in   Coal   Piles.— The  United  States  Navy 
Department  records  show  only  five  or  six  fires  in  coal  piles 
as  having  occurred  in  a  period  of  probably  20  years.     Infor- 
mation furnished  by  a  number  of  firms  using  large  quantities 
of  coal,  was  mostly  of  a  negative  character,  as  they  had 
never  experienced  spontaneous  ignition  in  their  own  coal 
piles. 

The  Pacific  Mail  Steamship  Company  has  had  trouble  in  its 
coal, piles,  but  found  it  due  to  sulphur,  and  after  assuring  the 
absence  of  this  ingredient  has  had  no  further  trouble,  whether 
the  coal  was  wet  or  dry.  Other  firms  have  stated  that  in  the 
rare  cases  of  spontaneous  ignition  in  coal  piles,  within  their 
experience,  they  believe  them  due  to  the  presence  of  sulphur. 

61.  Precautions  in  Storage  of  Bituminous  Coal  to 
Prevent  Spontaneous  Ignition. — Professor  Lewes's  rec- 
ommendations on  coal  storage  are  as  follows:     "The  coal 
store  should  be  well  roofed  in,  and  have  an  iron  floor  bedded 
in  cement;  all  supports  passing  through  and  in  contact  with 
the  coal  should  be  of  iron  or  brick;  if  hollow  iron  supports 
are  used,  they  should  be  filled  solid  with  cement.     The  coal 
must  never  be  loaded  or  stored  during  wet  weather,  and  the 
depth  of  coal  in  store  should  not  exceed  8  feet,  and  where 
possible,  should  only  be  6  feet.     Under  no  conditions  must 
a  steam  or  exhaust  pipe  or  flue  be  allowed  in  or  near  any 
wall  of  the  store,  nor  must  the  store  be  within  20  feet  of  any 
boiler,    furnace,   or  bench    of   retorts.     No  coal  should  be 
stored  or  shipped  to  distant  ports  until  at  least  a  month  has 
elapsed  since  it  was  brought  to  the  surface.     Every  care 
should  be  taken  during  loading  or  storing  to  prevent  break- 
ing or  crushing  of  the  coal,  and  on  no  account  must  a  large 
accumulation  of  small  coal  be  allowed.     These  precautions, 
if  properly  carried  out,  will  amply  suffice  to  entirely  do  away 
with  spontaneous  ignition  in  stored  coal  on  land." 

62.  Extinguishing  a  Coal-Pile  Fire. — When  a  coal 
pile  has  ignited,  the  best  way  to  extinguish  trje  fire  is   to 
remove  the  coal,  spread  it  out,  and  then  use  water  on  the 
burning  part.     The  incandescent  portion  is  invariably  in  the 


36  FUELS  §16 

interior,  and  when  the  fire  has  gained  any  headway  usually 
forms  a  crust,  if  the  coal  is  bituminous,  that  effectually  pre- 
vents the  water  from  acting  efficiently. 


COAL    DUST    AS    FUEL, 

63.  Coal  dust,  when  mixed  in  air,  burns  with  such  extreme 
rapidity  as  in  some  cases  to  cause  explosions.     Coal  may  be 
burned  without  smoke,  and  with  high  economy  if,  instead  of 
being  introduced  into  the 'firebox  in  the  ordinary  manner, 
it  is  first  reduced  to  a  powder  by  pulverizers,  and  if,  instead 
of  the  ordinary  boiler  firebox,  there  is  a  combustion  chamber 
in  the  form  of  a  closed  furnace  lined  with  firebrick  and  pro- 
vided with  an  air-injector  nozzle  similar  in  construction  to 
those   used   in   oil-burning   furnaces.     The  nozzle  throws  a 
constant  stream  of  the  fuel  into  the  chamber,  and  is  so  located 
that  it  scatters  the  powder  throughout  the  whole  space  of  the 
firebox.     When  this  powder  is  once  ignited,  which  is  readily 
done  by  first  raising  the  lining  to  a  high  temperature  by  an 
open   fire,  the    combustion   continues   in   a   regular  manner 
under  the  action  of  the  current  of  air  that  carries  in  the  fuel. 

Powdered  fuel  has  recently  been  adopted  successfully  in 
this  country  in  the  rotary  kilns  used  in  the  manufacture  of 
Portland  cement. 

64.  The  best  results  in  burning  coal  dust  can  only  be 
obtained  when  the  following  essentials  are  complied  with, 
viz.:     (1)  The  fuel  must  be  reduced  cheaply  to  a  very  finely 
divided  powder  and  must  be  of  a  strictly  uniform  grade  and 
size,  and  must  be  equally  dry  throughout;    and  the  drier  the 
better.     (2)   The  coal  powder  mixed  with  air  must  be  car- 
ried in  an  unbroken   stream  into  the  combustion  chamber. 
(3)  The  air-current  must  be  so  regulated  that  it  will  hold 
the   coal  powder   in   suspension,   when  within   the   furnace, 
until  complete  combustion  is  effected.      (4)    A  sufficiently 
high  temperature  must  be  continuously  maintained  in  the 
furnace,  to  insure  perfect  combustion  of  the  powder. 

The  problem  of  how  to  reduce  the  coal  economically  to 
the  required  standards  of  fineness  and  uniformity  is  the  one 


§16 


FUELS 


37 


thing  that  has  given  great  trouble  in  developing  new  devices 
in  firing-apparatus. 

65.  The  advantages  of  the  use  of  powdered  fuel  may  be 
summarized  as  follows:  (1)  The  economical  and  complete 
combustion  of  the  fuel;  (2)  complete  smokelessness;  (3) 
reduced  labor  expenses,  since  one  man  can  easily  manage 
several  furnaces;  (4)  adaptability  and  ease  of  regulation  to 
meet  any  requirements,  especially  when  the  work  is  that  of 
steam  generation;  (5)  decreased  wear  and  tear  of  furnaces 
in  the  case  of  internally  fired  boilers;  (6)  saving  of  time  in 
starting  up  furnaces,  and  rapid  stoppage  of  firing  in  case  of 


necessity;  (7)  less  labor  in  removing  refuse,  which  is  small 
in  quantity  and  in  the  form  of  slag;  (8)  intimate  contact  of 
the  fuel  with  the  air,  whereby  a  minimum  excess  of  air  over 
the  theoretical  volume  required  is  employed,  and  waste  of 
heat  thus  avoided. 

66.  Coal-Dnst  Burner. — Fig.  1  shows  the  general 
arrangement  of  the  Rowe  system  of  feeding  dust  into  a  fur- 
nace. The  coal  is  ground  to  a  dust,  dried,  and  conveyed  to  a 
storage  hopper,  and  is  ready  for  delivery  into  the  blast  pipe. 
a  is  the  storage  hopper  for  the  coal  dust;  &,  a  fan  that  receives 
hot  air  from  the  pipe  c  and  delivers  it  into  the  air  spout  /. 


38  FUELS  §  16 

The  conveyer  d  carries  the  coal  dust  from  the  bottom  of  the 
hopper  a  and  delivers  it  into  the  air  spout  /  just  in  front  of  the 
nozzle  <?,  which  serves  to  concentrate  the  air  so  that  it  is  thor- 
oughly mixed  with  the  dust.  At  g,  is  a  second  nozzle  for 
thoroughly  mixing  the  dust  and  air  just  before  it  enters  the 
furnace.  The  feed-spout  h  is  made  of  cast  iron  and  has  a  semi- 
circular opening  so  as  to  spray  the  dust  against  the  arch  wall, 
where  it  is  ignited  and  burned  in  suspension.  The  coal  dust 
is  ignited  by  contact  with  the  walls  of  the  furnace,  which  have 
been  heated  by  a  fire  on  the  grate.  This  system  can  be  used 
with  any  furnace  without  alteration  of  the  grates;  and  in  case 
of  accidents,  coal  can  be  fed  at  the  furnace  doors  the  same 
as  before.  

PRESSED    FUEL,,   OB    BRIQUETS 

67.  Finely  crushed- coal  mixed  with  warm  pitch  or  other 
cementing  material  may  be  pressed  by  machinery  into  blocks 
or  briquets;  these  make  a  very  good  fuel  when  the  coal  from 
which  they  are  made  is  of  good  quality.     The  dust,  or  culm, 
that  is  thrown  away  at  the  anthracite  mines  might  thus  be 
made  into  valuable  fuel,  but  attempts  thus  far  to  use  it  have 
generally  proved  commercially  unsuccessful  in  America,  on 
account  of  the  cost  of  manufacture  and  the  low  prices  of 
marketable  coal.     In  Europe,  however,  the  manufacture  of 
briquets  from  coal  dust  is  quite  a  large  industry. 

68.  The  following  are  some  of  the  advantages  claimed 
for  briquets:  They  are  sound  throughout  and  will  not  decrep- 
itate while  burning,  thus  reducing  the  loss  by  fine  material 
working  through  the  grates.    The  bond,  if  properly  selected, 
renders  the  briquets  practically  waterproof,  so  that  they  are 
not  injured  if  kept  in  storage,  do  not  evolve  combustible 
gases  nor  ignite  from  spontaneous  combustion.    There  is  no 
fine  material  mixed  with  the  briquets,  and  hence  a  more  uni- 
form fire  can  be  maintained  with  them.     They  can  be  made 
of  such  a  form  as  to  occupy  less  space   than  the  original 
fuel.     The  French  navy  has  found  it  possible  to  store  10  per 
cent,  more  briquets  than  coal  in  a  given  space,  and  also  that 
the  loss  by  breakage  and  pulverization  is  very  much  less. 


§  16  FUELS  39 

69.  In   Germany,  the   briqueting   of   lignite,  peat,   etc. 
has  reached  its  greatest  development.     The  crude  lignite  is 
crushed  and  pulverized;   it  is  then  heated  by  steam  until  it 
is  plastic,  when  it  is  carried  to  the  machine  press,  where  it  is 
pressed,  between  heated  iron  jaws,  into  hard,  firm  briquets. 

The  present  tendency  is  to  employ  no  inorganic  bonding 
materials,  as  they  increase  the  ash.  The  material  to  be 
briqueted  should  be  as  clean  and  free  from  dirt  or  slate  as 
possible,  and  the  particles  should  be  of  practically  uniform 
size.'  In  Europe,  it  is  considered  that  a  lignite  for  briquet- 
ing  should  contain  about  45  per  cent,  of  water,  so  that  after 
it  is  dried  it  will  contain  just  the  proper  amount  needed  to 
form  the  briquet. 

The  briqueting  of  peat  has  become  an  important  industry 
in  some  localities  where  it  can  compete  with  other  fuels. 
It  may  be  compressed  with  or  without  the  admixture  of  other 
inflammable  materials  such  as  bituminous  coal  dust,  anthra- 
cite culm,  or  dry  sawdust. 

70.  Machines  for  Briqueting  Fuel. — Fuel,  fuel  dust, 
and  other  products  may  be  briqueted  by  a  number  of  styles 
of  machines,  but  all  these  may  be  divided  into  two  classes, 
briquet  and  eggette  machines.     The  eggette  machines  have 
a  pair  of  rollers,  the  faces  of  which  are  provided  with  semi- 
spherical  or  semiovoid  openings.     The  material  that  is  fed 
between  these  rolls  crowds  into  the  openings  of  the  two  rolls, 
thus  forming  small   spheres.     The   material  is   thoroughly 
mixed  with  a  suitable  bond  before  being  fed  to  the  rolls,  and 
the  eggettes  are  received  on  any  suitable  form  of  traveling 
belt  or  chute  and  removed  for  drying  or  storage.     The  bri- 
queting machines  all  act,  more  or  less,  on  the  principle  of 
the  brick  machine,  having  some  kind  of  a  die  or  mold  into 
which   the   material    is   crowded.     The    material    is    either 
pressed  as  it  is  being  fed  into  the  mold  or  subsequently  by 
some  form  of  plunger.     For  some  materials,  common  brick 
machines,  such  as  are  used  in  the  manufacture  of  building 
brick,   are   employed;    while   in   others,  special   forms   are 
necessary. 

145—26 


40 


FUELS 


COKE 

71.  Coke  is  the  solid  material  left  after  driving  off  the 
volatile  portion  of  a  coal.  In  general,  there  are  two  classes 
of  coke:  (1)  gas-house  coke,  which  is  the  residue  left  in  the 
retort  after  the  gases  have  been  expelled  in  the  manufacture 
of  coal  gas;  (2)  oven  coke,  which  is  made  in  the  beehive  or 
by-product  retort  oven.  The  manufacture  of  coke  in  the 
beehive  and  retort  ovens  is  fully  described  in  Principles  ot 
Coking,  Coking  in  the  Beehive  Oven,  and  By-Product  Coking. 

Gas-house  coke  is  partly  used  in  heating  the  ret'orts  in  which 
the  coal  is  placed  in  making  coal  gas;  another  portion  is 
used  in  the  manufacture  of  water  gas,  and  some  is  sold  for 
fuel  purposes. 

The  coke  made  in  beehive  and  retort  ovens  is  divided 
into  two  classes:  furnace  coke,  which  is  used  in  blast-furnace 
smelting,  and  foundry  coke,  which  is  used  in  melting  iron  in 
the  foundry  cupola.  Probably  95  per  cent,  of  all  the  coke 
produced  is  used  in  blast  furnaces  and  foundries. 

Coke  is  also  sometimes  crushed  and  sized  similar  to 
anthracite  and  used  as  a  domestic  fuel  in  competition  with 
anthracite.  The  demand  for  coke  in  the  manufacture  and 
melting  of  iron  is,  however,  so  great  that  very  little  prog- 
ress has  thus  far  been  made  in  introducing  it  as  a  domestic 
fuel.  Table  XIV  gives  analyses  of  a  few  standard  cokes. 

TABLE   XIV 
ANALYSES    OF    COKE 

{From  report  of  John  R.  Procter,  Kentucky  Geological  Survey) 


Where  Made 

Fixed 
Carbon 

Ash 

Sulphur 

Cotmellsville,  Pa.,  average  of  3  samples  .    .    . 

88.96 

9-74 

.810 

Chattanooga,  Tenn.,  average  of  4  samples  .    . 

80.51 

16.34 

1-595 

Birmingham,  Ala.,  average  of  4  samples     .    . 

87.29 

10.54 

I-I95 

Pocahontas,  Va.,  average  of  3  samples    .    .    . 

92.53 

5-74 

•597 

New  River,  W.  Va.,  average  of  8  samples  .    . 

92.38 

7.21 

.562 

Big  Stone  Gap,  Ky.,  average  of  7  samples  .    . 

93-23 

5.69 

•  749 

§  16  FUELS  41 


LIQUID  FUELS 


PETRCXLETJM 

72.  Advantages  and  Disadvantages  of  Petroleum 
as    a   Fuel. — Next   to    natural    gas,    the    use    of   which   is 
restricted  to  a  few  localities,  petroleum  is  the  ideal  fuel. 
One  pound  of  it  has   a  heating  value  about  50  per  cent, 
greater  than  an  average  pound  of  coal.     It  may  be  trans- 
ported  with    great    facility    in   pipes,   tank   cars,   and   tank 
vessels,  and  it  may  be  burned  under  steam  boilers  or  in  heat- 
ing furnaces  without  smoke  or  ashes,  and  with  a  great  saving 
of  labor  as  compared  with  coal. 

Its  chief  disadvantages  are  its  limited  supply  and,  in  most 
localities,  its  price.  The  total  petroleum  output  of  the  United 
States  in  1900  was  63,362,704  barrels,  equal,  if  all  had  been 
used  as  fuel,  to  about  20,000,000  tons  of  coal,  but  the  greater 
portion  of  it  found  a  more  valuable  use  in  the  manufacture  of 
lubricating  and  illuminating  oils,  and  other  products.  It  is 
not  probable  that  the  oil  wells  of  the  world  will  ever  con- 
tribute more  than  1  or  2  per  cent,  of  the  total  fuel  supply. 

73.  In  many  parts  of  the  world  in  which  coal  is  expen- 
sive, as  in  California,  Texas,  Mexico,  and  South  America, 
petroleum  will  be  largely  used  in  place  of  coal  on  account  of 
its  relatively  lower  price.     The  possibility  of  economically 
substituting   petroleum   for  coal    as  fuel   in  any  particular 
place    depends  chiefly   on   the   relative  prices   of   the    two 
fuels  at  that  place,  and  as  the  prices  of  both  fuels  are  con- 
tinually varying,   there  may   be  some  years  at  any  given 
place  when  it  is  more  economical  to  use  oil,   and   others 
when  it  is  more  economical  to  use  coal. 

74.  Heating   Value. — The    average    heating  value  of 
crude  petroleum  is  about  20,000  B.  T.  U.  per  pound  or  147,400 


42 


FUELS 


§16 


B.  T.  U.  per  gallon.     The  heating  value  of  a  pound  of  coal 
is  from  about  10,000  to  15,000  B.  T.  U. 

75.  One  barrel  of  petroleum  contains  42  gallons.  Taking 
the  specific  gravity  of  petroleum  as  .885,  1  gallon  weighs 
7.37  pounds  and  1  barrel,  42  X  7.37  =  310  pounds,  nearly. 
From  this,  the  relative  value  of  a  barrel  of  oil  and  a  ton 
(2,000  pounds)  of  coal  as  given  in  Table  XV  is  found. 

TABLE    XV 


Thermal  Value  of 
Different  Coals 
B.T.U.  per  Pound 

Pounds  of  Coal 
Equivalent  to 
i  Pound  of 
Petroleum 

Pounds  of  Coal 
Equivalent  to 
i  Barrel  of 
Petroleum 

Barrels  of  Petro- 
leum Equiva- 
lent to  i  Ton 
of  Coal 

IO,OOO 

2.OOO 

620 

3-23 

II.OOO 

1.818 

564 

3-55 

I2.OOO 

1.667 

517 

3.87 

I3,OOO 

1.538 

477 

4.19 

14,000 

1.429 

443 

4-52 

15.000 

1-333 

413 

4.82 

If  we  take  an  average  coal  at  12,400  B.  T.  U.  per  pound, 
which  would  represent  an  anthracite  with  about  15  per  cent, 
of  ash  and  moisture,  a  ton  of  average  coal  is  equivalent  to 
4  barrels  of  oil. 

The  figures  in  Table  XV  represent  what  may  be  called  the 
theoretical  relative  values  of  petroleum  and  coal.  They  are 
also  the  practical  relative  values  if  the  two  fuels  cost  the 
same  for  labor  in  handling,  storage,  insurance,  etc.,  and  if 
they  are  burned  with  equal  efficiency  in  the  furnaces.  These 
conditions  vary  considerably  in  different  cases.  In  ocean 
steamers,  for  instance,  there  is  a  great  advantage  in  favor  of 
petroleum  on  account  of  the  carriage  being  cheaper,  since 
for  a  given  heating  value  only  about  two-thirds  of  the  weight, 
on  an  average,  has  to  be  stored  and  carried.  There  is  also 
a  great  saving  of  labor  in  the  handling  of  the  fires,  and  the 
troubles  due  to  ash  and  clinker  are  avoided. 


§  16  FUELS  43 

EXAMPLE  1.—  If  a  coal  having  a  heating  value  of  12,000  B.  T.  U.  per 
pound  is  worth  $3  per  ton  of  2,000  pounds,  what  is  crude  petroleum, 
having  a  heating  value  of  20,000  B.  T.  U.  per  pound,  worth  per  barrel 
of  310  pounds  if  both  fuels  can  be  burned  with  equal  efficiency  and 
cost  the  same  for  handling? 

SOLUTION.  —  The  heating  value  of  1  ton  of  the  coal  is  12,000  X  2,000 
=  24,000,000  B.  T.  U.  With  the  coal  worth  $3  per  ton,  1  cent  will 

buy  24'°pO:000    =  8o,000  B.T.U.     The  heating  value  of  1   barrel  of 

oUU 

petroleum  is   20,000  X  310  =  6,200,000  B.  T.  U.     Hence,   1  barrel  is 

'     6,200,000 
W0rth  "80^000"  =  '7ict'     AnS> 

EXAMPLE  2.  —  Under  the  conditions  in  example  1:  (a)  how  many 
pounds  of  coal  are  equivalent  to  a  barrel  of  oil?  (6)  How  many 
barrels  of  oil  are  equivalent  to  a  ton  of  coal? 


SoLUTiON.-(fl)         'QOO       =  516|  Ib.    Ans. 
(6)          |^  =  3.87bbl.    Ans. 

76.  Composition  of  Petroleum.  —  Crude  petroleum  is 
a  mixture  of  hydrocarbons,  which  may  be  separated  by  dis- 
tillation at  different  temperatures;  thus,  gasoline  is  driven 
off  by  heating  from   140°  to   158°  F.;    a  light   benzine    or 
naphtha  at  from  158°  to  248°  F.;  heavier  benzines  at  248°  to 
347°  F.;  kerosene,  or  ordinary  illuminating  oil,   at  338°  F. 
and  upwards;  lubricating  oils  at  482°  F.  and  upwards;  par- 
affin wax  at  a  higher  temperature;  leaving  a  tarry  residuum 
that  may  be  further  distilled  until  nothing  but  a  small  quan- 
tity of  coke  remains  in  the  still. 

77.  Petroleum  is  composed  mainly  of  carbon  and  hydro- 
gen,  though  small  amounts  of   oxygen   and   nitrogen    are 
usually  present  and  sometimes  sulphur,  which  is  particularly 
annoying  to  the  refiner. 

Table  XVI    gives  the  composition   of   petroleums   from 
different  localities. 

78.  The  analyses  in  Table  XVII  are  by  fractional  distil- 
lation and  are  an  indication  of  the  value  of  the  oils  for  com- 
mercial purposes. 


TABLE   XVI 


Locality 

Specific 
Gravity 
at  o°  C. 

Elementary  Composition 

C 

H 

O  by 

Difference 

United  States 
California    
California    
California    
Kentucky     
Ohio  . 

.887 

.886 
.816 
.920 
.841 

•857 

•857 
.870 
.860 
•855 
.870 
.892 
.892 
.861 
.786 
.875 
•  923 
.827 
.927 
.901 
.882 
•938 
•954 

86.93 
86.62 
86.93 
85.20 
84.20 
86.30 
84.90 
82.00 
86.80 
84.30 
83.20 

81.30 
84-50 
83-50 
85-30 
82.20 
80.40 
85.70 
86.2O 
84.00 
83.80 
87.10 
83.60 
85.00 
83.00 
87.40 
86.60 
85-30 

11.82 
12.92 
I3-07 
I3-36 
13.10 
13.07 
13.70 
14.80 
I3.2O 
14.10 
13.20 

13.40 
I3-50 
12.90 
12.  6O 
12.  IO 
12.70 
12.00 
13-30 
13.40 
12.70 
12.00 
I4.OO 
1  1.  2O 
12.  2O 
12.  6O 
12.30 
II.  6O 

2.70 
•54 

I.  II 

.70 

1.40 
3.20 

1.  60 
3-6o 

2.30 

2.00 
3-60 
2.IO 
5-70 
6.9O 
2.30 
•50 
1.  80 
3-50 
.90 
2.40 
2.80 
4-80 
.IO 
I.IO 

3-io 

Ohio,  Mecca 

Pennsylvania1,  near  Franklin  .    .    . 
Pennsylvania,  Oil  Creek    

Texas,  Beaumont    

West  Virginia    
West  Virginia 

Foreign  Countries 
Canada,  W.  Canada   
Canada,  Petrolia  
China,  Fu-li-fu 

Galicia,  West  Galicia". 

Galicia,  East  Galicia  

Germany3,  Hanover    

Germany,  Pechelbronn  

Germany,  Schwabweiler    
Italy,  Parma      .       ... 

East  India,  Burmah    

Java,  Rembang    

Java,  Tjabados,  Fanga    
Java,  Gagor  .... 

Roumania  

Russia,  Baku4    

Russia,  Baku,  very  heavy   .... 
Russia    Baku 

'The  Pennsylvania  crude  oil  consists  principally  of  the  paraffins, 
with  a  small  percentage  of  the  aromatic  series  and  a  minute  quantity 
of  the  naphthenes  in  the  heavy  distillates.  All  American  petroleum 
contains  oxygen  and  sulphur  compounds  and  a  few,  also,  nitrogen 
compounds. 

"The  Galicia  oils  consist  of  mixture  of  paraffins,  naphthenes,  and 
aromatic  hydrocarbons. 

3The  German  oils  are  principally  paraffins,  containing  also  aromatic 
hydrocarbons  and  naphthenes. 

*The  Baku  oils  are  composed  of  naphthenes  and  a  few  other  hydro- 
carbons, as  well  as  oxygen  and  sulphur  compounds;  in  the  lighter 
fractions  small  quantities  of  paraffin  are  found. 


§16 


FUELS 


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46  FUELS  §  16 

79.  Uses  of  Petroleum. — Crude  oil,  as  well  as  its  vari- 
ous distillates,  may  be  used  as  fuel  if  proper  provision  is  made 
for  burning  it;  'but  since  the  gasoline  and  benzine  vapors 
that  it  gives  off  at  low  temperatures  form  explosive  mixtures 
with  air,  it  is  not  a  safe  fuel  to  be  kept  in  storage;  therefore, 
these  vapors  should  be  distilled  from  it  before  it  is  shipped. 

Gasoline  and  benzine  are  used  as  fuel  for  oil  engines,  and 
as  fuel  for  steam  boilers  of  small  pleasure  yachts,  but  they 
must  be  handled  with  great  care  to  avoid  leakage  and  con- 
sequent danger  of  fire  and  explosion. 

By  blowing  air  into  either  crude  oil  or  its  lighter  distil- 
lates, such  as  naphtha,  it  becomes  charged  with  light  oil 
vapors,  and  may  be  used  like  a  gas  in  gas  engines  or  for 
other  fuel  purposes. 

Kerosene  makes  an  excellent  fuel  for  small  oil  stoves,  and 
for  oil  engines  that  are  especially  made  for  its  use,  but  it  is 
generally  too  expensive  to  be  used  on  a  large  scale,  where 
cheap  fuel  oils,  residuum;  etc.  are  available. 


METHOD  OF  BURNING  PETROLEUM 

80.  Although  the  use  of  liquid  fuel  for  steam  making 
has  not  become  general,  it  is  constantly  growing  in  favor. 
When  burned  in  properly  constructed  burners  its  combustion 
is  complete,  giving  no  smoke  and  no  ash.     It  can  be  burned 
under  any  boiler  with  very  little  alteration  of  the  furnace  so 
that  in  case  of ,  accident  the  firing  may  be  continued  with 
coal  with  but  little  delay.      For  the  successful  burning  of 
petroleum  without  smoke,  it  is  apparent  that  the  combus- 
tion   must   be    complete    in   the  furnace.       To    accomplish 
this,  there  must  not  only  be  a  sufficient  air  supply,  but  the 
fuel  must  be  in  a  finely  divided  condition  and  intimately 
mixed  with  the  air.     Under  these  conditions,  the  combustion 
will  be  instantaneous  and  complete.     The  spray  is  produced 
by  means  of  atomizers  of  various  designs. 

81.  Numerous  forms  of  petroleum  burners  are  on  the 
market,  but  all  are  designed  to  effect  an  atomization  of  the  oil 
and  to  mix  it  thoroughly  with  air.     When  properly  operated, 


§  16  FUELS  47 

any  one  of  these  forms  is  efficient.  The  form  or  type  of 
burner  is  less  essential  than  the  furnace  in  which  it  is 
used,  or  than  the  proper  regulation  of  the  supply  of  oil  and 
air.  The  most  common  forms  of  burners  use  a  jet  of  steam 
at  high  pressure  for  spraying  the  oil  and  for  inducing  a  cur- 
rent of  air  to  mix  with  the  spray.  Air  compressed  to 
15  pounds  per  square  inch,  or  upwards,  may  be  used  instead 
of  steam.  The  only  advantage  of  steam  is  the  facility  with 
whjch  it  may  usually  be  obtained.  Its  disadvantage  is  that 
it  costs  not  only  the  heat  required  to.  generate  it,  but  the 
heat  required  for  superheating  it  to  the  temperature  at  which 
it  finally  escapes  in  the  chimney.  In  driving  a  steam  boiler 
with  oil  fed  by  a  steam  jet,  the  jet  may  require  as  much  as 

10  per  cent,  of  the  whole  quantity  of  steam  generated  by  the 
boiler,  or  much  more  than  would  be  required  to  run  an  air 
compressor  supplying  an  air  jet.     Petroleum  burners  driven 
by  air  jets  produce  a  higher  temperature  than  those  driven 
by  steam  jets. 

Petroleum  burners  may  be  divided  into  two  general  classes, 
the  flat-jet  and  the  injector. 

82.  Flat-Jet  Burners. — Two  forms  of  the  flat-jet  type 
are  shown  in  Figs.  2  and  3.     Fig.  2  is  a  form  that  consists 
of  two  tubes  fastened  together.     In  this,  a  is  the  oil  pipe; 
d,  a  cock  for  regulating  the  supply  of  oil;  c,  the  steam  pipe; 
d,  the  steam  valve;  e,  a  guard  around  the  pipe  to  guide  the  oil 
over  the  steam  jet. 

A  stream  of  oil 
flows  from  the  supply 
tank  through  a  and  is 
distributed  in  a  thin 
sheet  over  the  jet  of  FlG-  2 

steam,  with  the  result  that  the  oil  is  carried  forwards  in  the 
form  of  a  finely  divided  spray.  By  changing  the  shape  of  the 
jet  of  steam,  different  shapes  may  be  given  to  the  flame. 

83.  The  other  form  of  the  flat-jet  burner,  Fig.  3,  has  an 

011  passage  a  below  which  is  the   steam  passage  b.     The 
burner  is  tapped  at  the  side  for  a  ll-inch  oil  pipe  at  c  and  a 


48 


FUELS 


i-inch  steam  pipe  at  d.     The  oil  coming  through  the  pas- 
sage a  falls  directly  on  the  steam  shooting  through  the  narrow 

slit  e  at  the  end  of  the  pas- 
sage b  and  is  completely 
atomized.  Two  holes  at  the 
back  of  the  burner  are  closed 
by  plugs  m,  n,  which  are  re- 
moved for  cleaning. 

Fig.  4  shows  the  arrangement  of  this  burner  in  a  locomotive 
firebox.  The  back  damper 
is  completely  closed,  and  a 
large  front  damper  with 
about  2  square  feet  of  super- 
ficial opening  is  arranged 
in  front.  A  plate  with  an 
air  opening  20  by  14  inches 
supports  the  firebrick  at 
the  back  of  the  firebox, 
which  receives  the  vapor- 
ized oil.  The  supply  of  air  FlG- 4 
is  regulated  by  the  front  damper,  and  the  supply  of  oil  by  a 


wheel  valve  in  the  cab.    With  the  air  and  oil  under  perfect 
control,  there  is  no  difficulty  in  obtaining  perfect  combustion. 


§16 


FUELS 


49 


84.  Injector  Oil  Burners. — Of  the  injector  type  of  oil 
burner,  the  one  invented  by  Thomas  Urquhart  and  used  on 
locomotives  in  Russia  many  years  ago,  as  shown  in  Fig.  5, 
is  a  fair  example.  The  oil  runs  down  a  pipe  a  that  ends  in 
the  external  nozzle  b  of  the  injector,  while  the  steam  passes 
through  the  inner  nozzle  c,  which  it  enters  through  a  ring  of 
holes  d,  the  steam  and  oil  cavities  being  separated  by  a 
stuffingbox  packed  with  asbestos.  The  steam  supply  is  reg- 
ulated by  a  valve  and  the  oil  supply  by  screwing  the  steam 


nozzle  backwards  and  forwards  in  the  external  nozzle  by  means 
of  a  worm-wheel  e,  thus  varying  the  size  of  the  annular  passage 
between  the  two  nozzles  d,  c.  The  amount  of  steam  required 
to  operate  the  injector  on  the  Russian  railway,  according  to 
Mr.  Urquhart,  is  from  8  to  13  per  cent,  of  the  steam  made  by 
the  boiler,  the  higher  percentage  being  required  in  winter. 

85.     Fig.  6  (a)  and  (6)  shows  the  Kirkwood  burner  or 
atomizer.     The  oil  enters  through  the  opening  shown  and 


50 


FUELS 


§16 


passes  through  the  inner  nozzle  a,  when  it  comes  in  contact 
with  the  steam  jet,  which  vaporizes  the  oil  and  projects  'it 
through  the  nozzle  b  into  the  furnace.  The  amount  of,  oil 
passing  through  a  is  regulated  by  the  handle  c,  which  opens 
or  closes  the  valve  d,  the  disk  e  indicating  the  amount  the 
valve  is  open.  Similarly,  by  means  of  the  handle  /,  the 
steam  passage  g  may  be  regulated,  the  amount  of  opening 
being  indicated  by  the  disk  h. 

86.     Fig.  7  shows  a  burner  in  which  the  oil  is  atomized 
by  compressed  air  at  a  pressure  of    about  15   pounds  per 


square  inch.  Lower  pressures  have  been  found  insufficient 
to  properly  atomize  the  oil.  The  oil  centers  through  the 
right-hand  valve,  follows  the  course  of  the  arrow  leading 
from  the  chamber  marked  Oil  until  it  reaches  the  end  of  the 
central  nozzle,  where  it  is  vaporized  by  a  stream  of  compressed 
air  which  enters  through  the  left-hand  valve,  passes  through 
the  chamber  marked  Air,  and  flows  down  the  central  nozzle. 

87.  Fig.  8  shows  a  method  of  installing  an  oil-burning 
system  in  a  steam-boiler  plant,  designed  by  The  International 
Gas  and  Fuel  Company,  of  Chicago.  Four  ducts  of  hollow 


§16 


FUELS 


51 


tile  a,  are  laid  in  the  ash-pit,  extending  nearly  to  the  bridge- 
wall;  the  ash-pit  door  openings  are  closed  by  brickwork  b 
above  the  outer  ends  of  the  tile.  The  forward  grate-bar 
bearer  is  dropped,  about  half  the  forward  set  of  bars  removed, 
and  a  course  of  firebrick  laid  with  fireclay  over  the  upper 
surface  of  the  grate.  Air  entering  through  the  tiles  passes 
under  the  grates  to  an  opening  in  front,  then  into  the 
combustion  chamber.  .The  spray  of  burning  oil  strikes  a 


checkerwork  of  loose  firebrick  built  over  the  rear  part  of  the 
grates.  The  fire-doors  are  closed  with  brick,  excepting  small 
openings  for  the  burner  nozzles  and  for  lighting  the  burners. 
Oil  is  delivered  from  barrels  through  the  pipe  d  into  a 
closed  tank  c  sunk  in  the  ground;  e  is  a  vapor  vent  pipe.  A 
steam  pump  /  draws  oil  through  the  strainer  g  and  pipe  h 
and  delivers  it  to  the  stand  pipe  z,  whence  it  flows  by  the 
pipe  j  to  the  burner  under  a  head  of  about  10  feet.  The 


52  FUELS  §  16 

pump  runs  constantly,  and  the  surplus  oil  flows  back  to  the 
tank  c  through  the  pipe  k.  A  device  /  having  a  piston  con- 
nected by  a  chain  with  a  cock  m,  automatically  opens  the 
cock  to  empty  the  stand  pipe  when  the  boiler  is  not  under 
steam  pressure.  The  exhaust  pipe  n  passes  through  the 
tank,  to  heat  the  oil  in  cold  weather.  A  blow-off  pipe  o 
drains  the  burner  steam  pipe  of  water.  At  the  point  where 
the  steam  and  oil  mix,  hot  air  is  supplied  to  the  burners  by 
the  pipe  q,  which  passes  through  the  fire-door  into  a  brick 
flue  over  the  grate  and  down  into  the  ash-pit.  The  steam 
going  to  the  burner  flows  through  a  coupling  r  containing 
a  perforated  disk;  the  duplex  gauge  £  shows  the  pressure  on 
each  side  of  the  orifice  in  this  disk. 


GASEOUS    FUELS 

88.  The  different  gases  used  as  fuel  are  the  following, 
arranged  in  the  order  of  their  heating  value:  (a)  Natural  gas, 
which  is  obtained  from  wells  in  different  parts  of  the  world; 
(b)  illuminating  gas,  or  coal  gas,  which  is  made  either  by 
distilling  coal  in  retorts  or  by  enriching  water  gas  with  the 
volatile  matter  distilled  from  cannel  coal  or  with  vapors  dis- 
tilled from  petroleum;  (c)  coke-oven  gases,  which  are  mainly 
those  coming  from  by-product  ovens,  as  explained  in  the 
Sections  on  coking,  although  occasionally  the  gases  from  the 
beehive  ovens  are  used  under  boilers;  (d)  water  gas,  which  is 
made  by  blowing  steam  through  a  bed  of  glowing  anthracite 
or  coke,  by  the  reaction  C +  H*O  =  CO  +  2//;  (e)  producer 
gas,  which  is  made  by  blowing  air  into  burning  bituminous 
coal,  in  which  case  the  volatile  matter,  including  condensable 
tarry  vapors,  is  distilled,  and  the  coke  is  burned  to  carbon 
monoxide;  producer  gas  is  also  made  by  blowing  air  into 
burning  anthracite,  thus  producing  carbon  monoxide;  (/)  com- 
bined water  gas  and  producer  gas,  which  is  made  by  blowing 
air  mixed  with  steam  into  a  producer  charged  with  burning 
bituminous  coal;  (g)  blast-furnace  gas,  which  is  the  waste 
gas  coming  from  the  top  of  a  blast  furnace,  and  which  con- 
tains a  certain  amount  of  carbon  monoxide  available  as  fuel. 


§16 


FUELS 


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Marsh  gas  (methane)  CH 

CHH*n  gases  

Carbon  monoxide,  CO  .  . 

Carbon  dioxide,  CO,  .  . 
Nitrogen,  JV  
Total  volume  (approxima 
Total  combustible  gases 
Heating  value  (B.  T.  U. 

64  FUELS  §  16 

89.  Table  XVIII  shows  the  composition  and  heating 
value  of  different  gases,  as  given  by  H.  A.  Humphrey  in  the 
Proceedings  of  the  Institution  of  Civil  Engineers  of  Great 
Britain,  1897. 

90.  Table  XIX  gives  some  additional  analyses  of  natu- 
ral, producer,  and  coke-oven  gases,  together  with  their  aver- 
age heating  values. 

91.  Blast-furnace  gas  varies  greatly  in  its  composition, 
and  in  six  analyses  made  in  1  day,  the  carbon  dioxide  varied 
from  6.6  to  7.7  per  cent.,  the  carbon  monoxide  from  20.1  to 
31.7   per   cent,    and    the  nitrogen    and  hydrocarbons   from 
60.5  to  72.2  per  cent,  by  volume.     The  heating  value  calcu- 
lated from  the  average    analyses  was  1,175  B.  T.  U.  per 
pound,  and  at  the  temperature  of  584°  F.,  at  which  it  entered 
the  steam  boiler  furnace,  it  carried  140  B.  T.  U.  per  pound 
additional  heat.     The  1,175  B.  T.  U  per  pound  are  equal  to 
about  94  B.  T.  U.  per  cubic  foot,  measured  at  32°  F.,  or  only 
about  one-tenth  of  the  value  of  a  cubic  foot  of  natural  gas. 

92.  As  shown  by  Tables  XVIII  and  XIX,  all  the  fuel 
gases  are  mixtures  of  several  gases.     The  gases  highest  in 
heating  value  contain  the  largest  percentages  of  hydrogen  and 
hydrocarbons;  and  those  lowest  in  heating  value  contain  the 
largest  percentages  of  nitrogen  and  carbon  dioxide.     Pro- 
ducer gases  contain  all  the  nitrogen  of  the  air  blown  into 
the  producer  and  also  some  carbon  dioxide  on  account  of  the 
great  difficulty  of  burning  all  the  carbon  to  monoxide. 

93.  The  heating  value  per  pound  and  per  cubic  foot, 
measured  at  32°  F.,  and  atmospheric  pressure,  of  the  several 
constituents  of  a  mixed  fuel  is  given  in  Table  XX.     The 
figures  in  the  first  column  are  those  of  Favre  and  Silbermann 
excepting  in  the  two  cases  noted.     Other  heating  values 
differing  slightly  from  these  are  given  by  different  author- 
ities, owing  to  a  difference  in  the  experiments  by  which  the 
values  have    been   determined.     In    the    third   column   are 
shown  approximate  figures,  giving  B.  T.  U.  per  pound  of 
combustible,  that  are  within  the  limits  of  error  of  chemical 


§16 


FUELS 


55 


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56 


FUELS 


§16 


analyses  and  calorimetric  experiments,  and  may  be  used  in 
making  calculations. 

TABLE  XX 


Burned  in  Oxygen 

Approximate 

Substance 

Per  Pound 
B.  T.  U. 

Per  Cubic 
Foot 
B.  T.  U. 

Values 
per  Pound 
B.  T.  U. 

Hydrogen  to  H,O      .                 ... 

62,032 

346.75 

62,000 

Carbon  to  carbon  dioxide,  CO,  .    .    . 

14,544 

14,600 

Carbon  to  carbon  monoxide,  CO  .   . 

4,451 

4,450 

Carbon    monoxide,    CO,   to   carbon 

dioxide  COa,  per  unit  of  CO  .    .    . 

4,325 

338.00 

4,300 

Carbon    monoxide,    CO,    to  carbon 

dioxide,  CO,,  per  unit  of  carbon  C 

10,150 

Marsh  gas  (methane),  CHt,  to  H,O 

and  CO, 

21   511 

I  ,050.00 

Ethylene   (olefiant-gas)  ,  C,Ht,   to 

*  Jtj  *  J 

H,O  and  CO,  

21,344 

1,568.00 

Benzole  gas,  C,//.,  to  H,O  and  CO, 

17,847 

Acetylene,  C,//,,  to  H,O  and  CO,  . 

18,196* 

i,35i.6o 

Sulphur  to  SO, 

4,osot 

4,000 

*  Calculated, 
t  N.  W.  Lord. 

94.  The  equivalent  centigrade  values,  in  pound-calories, 
may  be  obtained  by  dividing  the  B.  T.  U.  by  1.8.  Thus,  62,000 

B.  T.  U.  =  62,0°-°-  =  34,444  pound-calories. 
1.8 

NOTE. — The  pound-calorie  is  the  amount  of  heat  necessary  to  raise 
the  temperature  of  1  pound  of  water  1°C.  The  French  calorie  is  the 
amount  of  heat  necessary  to  raise  the  temperature  of  1  kilogram 
(2.2  pounds)  of  water  1°  C.  When  the  term  calorie  is  used  in  this 
Section,  the  pound-calorie  is  meant. 


PRODUCER  GAS 

95.  The  producer  or  the  apparatus  in  which  producer 
gas  is  made,  is  a  cylindrical  riveted  shell  of  boiler  plate,  lined 
with  firebrick.  The  early  producers  were  made  rectangular 
in  section,  but  the  circular  section  was  adopted  as  offering 
many  advantages,  and  is  now  wholly  used.  The  principal 


§16 


FUELS 


57 


improvement  in  producers  since  the  original  Siemens  pro- 
ducer has  been  the  adoption  of  a  closed  bottom.  To  accom- 
plish this,  the  producer  proper  rests  in  a  water  pan,  through 
which  the  ashes  or  clinkers  are  raked  out.  This  water  acts 
as  a  seal,  preventing  the  escape  of  gas  and  the  introduction 


FIG.  0 

of  air,  which  occurred  in  the  old  producers  while  the  fires 
were  being  cleaned,  contributing  much  to  their  irregular 
working  and  the  poor  quality  of  gas.  Instead  of  being  flat, 
the  grate  is  conical,  and  underneath  it  the  pipe  conveying  air 
and  steam  terminates,  introducing  these  in  the  center  of  the 


58 


FUELS 


producer,  thus  insuring  an  even  and  regular  circulation  within 
the  chamber. 

96.  Forter  Water-Seal  Producer. — Fig.  9  shows  one 
of  the  most  successful  and  a  general  type  of  the  water-seal 
producer.  It  has  the  usual  brick-lined  shell  of  steel  a.  There 
are  usually  but  two  steam  jets  s  on  opposite  sides  to  introduce 
the  air  and  steam  into  the  wind  box  w  and  under  the  grate. 
In  this  one,  a  third  steam  jet  s'  forces  steam  and  air  into  the 
center  of  the  producer  by  means  of  a  pipe  terminating 
beneath  the  grate  d,  as  shown  at  b,  and  protected  from  ashes  by 
a  cone-shaped  hood.  The  wind  box  has  a  number  of  air-tight 
doors,  through  which  sections  of  the  grate  can  be  removed  to 
bar  out  any  large  clinkers  accumulating  on  the  bottom.  The 
ashes  drop  into  water  in  the  ash-pan  c  as  the  coal  is  burned, 
and  are  removed  from  time  to  time  without  interfering  with 
the  working  of  the  producer. 

TABL.E  XXI 


Proximate  Analysis 

Ultimate  Analysis 

i 

c 

S 

T3 

Number  o 
Sample 

Volatile  Mat 
Per  Cent. 

Fixed  Carb 
Per  Cent. 

Ash 
Per  Cent. 

Total  Carb( 
Per  Cent. 

Hydrogen 
Per  Cent. 

§SS 
g^u 

[M 

Ash 
Per  Cent. 

Sulphur 
Per  Cent. 

I 

36.20 

58.20 

5.60 

75-63 

4-30 

13.62 

5-60 

-85 

2 

34-70 

58.45 

6.85 

76.63 

4-57 

10.95 

6.85 

I.OO 

3 

32.80 

58.10 

9.10 

73-92 

4-73 

"•53 

Q.IO 

.92 

4 

33-75 

55-00 

11.25 

72.87 

4-76 

IO.IO 

11.25 

1.  02 

97.     Fuel    Employed    for    Making    Producer    Gas. 

Producer  gas  can  be  made  from  anthracite,  bituminous  coal, 
coke,  charcoal,  peat,  or  even  wood.  The  coal  used  should  be 
of  good  quality,  quite  free  from  sulphur,  if  the  gas  is  to  be  used 
in  steel  making,  and  should  have  a  low  or  moderate  percent- 
age of  ash,  and  be  of  such  a  character  as  not  to  clinker  on  the 
grate.  While  practically  all  bituminous  coals  (if  not  too  high 
in  sulphur)  maybe  used,  there  is  a  decided  difference  in  their 
value.  Proximate  and  ultimate  analyses  of  four  samples  of 


§  16  FUELS  59 

good  average  coal  for  producer  gas  are  given  in  Table  XXI. 
The  proximate  analysis  (with  the  sulphur)  is  all  that  is  neces- 
sary for  the  ordinary  valuation  of  a  coal  for  this  purpose. 

Ordinarily,  the  higher  the  coal  is  in  volatile  matter,  the 
richer  is  the  gas  produced,  as  it  contains  more  hydrocarbons. 
Sulphur  should  not  exceed  1  per  cent.,  but  this  depends  on 
its  condition  in  the  coal — if  it  is  in  such  a  combination  that  it 
is  mostly  oxidized,  remaining  with  the  ash  as 'sulphate,  it  may 
be, much  higher;  if  principally  volatilized,  even  this  amount 
may  allow  the  steel  to  absorb  too  much  of  it  from  the  gas. 

98.  Producer  Reactions. — The  reactions  that  take 
place  in  making  producer  gas  are: 

1.  Carbon  burned  to  carbon  dioxide, 

C+  O,  =  CO, 

2.  Reduction   of    the    CO,    by    the    hot    coal    to   carbon 
monoxide,  CO,  +  C  =  2CO 

3.  Incandescent  carbon  decomposing  water  vapor, 

H*0+C  =  CO+tf, 

On  the  grate  in  the  bottom  of  the  producer  are  the  ashes, 
which  serve  to  heat  the  steam  and  air;  and,  in  connection 
with  the  water  seal,  prevent  the  escape  of  gas  in  cleaning 
the  fires.  Next  above  this  is  the  bed  of  incandescent  fuel, 
where  the  air  and  steam  combine  with  the  carbon  in  the 
above  reactions.  On  top  of  this  is  the  section  where  distil- 
lation occurs.  The  temperature  is  constantly  lowered  by 
the  addition  of  fresh  coal,  but  the  heat  of  the  bed  beneath 
keeps  up  the  distillation  of  the  volatile  products  of  the  fuel. 
While  the  ash  oea  is  sharply  separated  from  the  bed  above, 
the  two  upper  beds  overlap  and  their  reactions  occur  to  a 
considerable  extent  in  the  same  reg;on. 

The  reactions  are  not  all  as  simple  as  expressed  in  the 
above  equations,  as  a  series  of  more  or  less  complicated 
processes  occur.  Under  certain  conditions,  part  of  the 
distillation  may  take  place  lower  in  the  hotter  section,  when 
the  original  hydrocarbons  will  be  partly  broken  up  and  new 
ones  formed.  The  production  of  gas  is  regulated  nearly 
automatically,  as  the  amount  of  gas  withdrawn  determines 


60  FUELS  §  16 

the  supply  of  air  to  the  grate — assuming,  of  course,  that  the 
producer  is  otherwise  properly  managed.  One  volume  of 
carbon  monoxide  produced  requires  2£  volumes  of  air  con- 
taining 2  volumes  of  nitrogen  to  pass  through  the  grate; 
1  volume  of  water  vapor  on  decomposition  gives  1  volume 
of  hydrogen  and  1  volume  of  carbon  monoxide. 

99.  Operation  of  the  Producer. — The  fuel  is  fed 
through  a  bell  and  hopper,  by  shoveling,  or  by  chutes  from 
overhead  storage  bins.  As  the  coal  in  the  producer  becomes 
hot,  it  partially  disintegrates  and  cakes,  forming  layers, 
through  which  the  air  is  forced  with  difficulty,  or  channels 
are  made  through  the  coal  so  that  a  large  part  of  the  carbon 
dioxide  first  formed  will  not  be  brought  in  contact  with  car- 
bon and  reduced  to  carbon  monoxide.  To  avoid  this,  "poke 
holes"  are  placed  in  the  top  of  the  producer,  through  which 
the  incandescent  mass  is  broken  and  stirred  with  long  pokers 
at  intervals  of  a  few  minutes.  Ashes  and  clinkers  are 
removed  about  every  other  day,  depending  on  the  quality 
of  the  fuel  and  the  rate  at  which  the  producer  is  driven. 
Other  conditions  being  right,  the  hotter  and  deeper  the  fire, 
the  better  the  reactions  take  place.  The  usual  depth  of  fire 
is  about  6  feet,  varying  with  the  ashes  on  the  grate  and  the 
rate  of  feeding  the  fuel.  If  the  fire  gets  much  deeper  than 
this,  it  is  impossible  to  keep  the  lower  part  of  it  broken  up, 
however  well  it  is  poked;  if  much  shallower,  the  carbon 
dioxide  and  water  vapor  are  not  decomposed. 


COAL  GAS 

100.  Coal  gas  is  made  by  heating  bituminous  coal  in 
Q  -shaped  fireclay  retorts  that  are  arranged  as  shown  in 
Fig.  10.  These  retorts  are  about  15  inches  high,  by  26  inches 
wide,  inside,  and  9  to  10  feet  long  if  single-ended,  or  18  to 
20  feet  long  if  double-ended.  The  retort  walls  are  about 
4  inches  thick  and  each  retort  is  connected  with  a  pipe  that 
allows  the  gas  to  escape  as  fast  as  formed. 

Three,  six,  or  nine  retorts,  depending  on  the  size  of  the 
works  are  generally  grouped  together  to  form  a  bench;  this 


§16 


FUELS 


61 


is  heated  by  a  single  furnace  placed  beneath  the  retorts.  A 
stack  consists  of  several  benches  built  side  by  side.  The 
fuel  for  heating  the  retorts  is  the  gas  coke  that  is  left  after 
the  gas  has  been  distilled  from  the  coal. 


FIG.  10 

101.  Operating  a  Bench. — The  retorts  are  first  heated 
to  a  red  heat  and  then  from  200  to  400  pounds  of  coal,  depend- 
ing on  the  size  of  the  retort,  is  put  in  with  a  long  shovel  and 
carefully  leveled.     The  mouth  of  the  retort  is  next  closed 
with  a  lid,  which  is  sealed  with  cement.     The  charge  remains 
in  the  retort  for  about  4  hours  when  the  lid  is  taken  off  and 
the  coke  pulled  out  by  a  rake. 

102.  Fig.  11  gives  a  general  idea  of  a  complete  coal- 
gas  plant.     The   gas,  which  is  drawn  from   the  retorts  by 
means  of  a  pump  or  an  exhauster,  passes  up  the  vertical  pipe 
shown  in  Fig.  11,  which  curves  downwards  into  the  hydraulic 
main  <?.    This  main  is  partly  filled  with  water,  which  cools  the 
gases  so  that  a  considerable  amount  of  the  tar  and  ammonia 
contained  in  them  is  condensed.     From  the  hydraulic  main, 
the  gas  passes  through  c ,  d  to  the  condenser  /,  which  removes 
the  balance  of  the  tar.     This  condenser  consists  of  curved 
pipes  that  are  either  cooled  by  the  air  or  else  by  water  sur- 
rounding them.     Gases  next  pass  through  the  scrubber  g, 
which  is  filled  with  coke  or  small  brushwood    over  which 
water  is  running.      This  water  further  cools  the  gas  and 


62 


FUELS 


§16 


removes  any  tar  that  has  not  been  removed  in  the  hydraulic 
main  e  or  in  the  condenser  /  and  also  takes  out  the  ammonia. 
The  gas  next  passes  through  the  purifier  />,  which  contains 
trays  of  dry  or  slightly  dampened  lime,  which  removes  the 
last  traces  of  impurities.  The  gas  then  passes  through  the 
pipe  /  into  the  gas  holder  q. 


LJ— 

U 

? 

, 

—  T^^frf 

1    % 

4 

III 

y 

\ 

*- 

^         i       i       i  IY 

'I    '    1    '    1     ' 

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jj.  jj.  j_  ' 

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^ 

103.     Gas  Coals. — Table  XXII  gives  analyses  of  typical 
American  gas  coals. 

TABLE   XXII 
GAS    COALS 


Westmoreland  Coal  Company 

Pennsylvania  Gas  Coal 
Company 

South  Side 
Mine 

Foster 
Mine 

Larrimer 
No.  2 

Irwin 
No.  i 

Irwin 

Sewickley 

Water   .... 

1.410 

1.310 

1.560 

I.78 

1.280 

1.490 

Volatile  matter 

37-655 

37-100 

39.185 

35-36 

38.105 

37-153 

Fixed  carbon 

54-439 

55-004 

54-352 

59-29 

54-383 

58.193 

Sulphur  .    .    . 

.636 

-636 

-643 

.68 

.792 

-658 

Ash    

5.860 

5-950 

4.260 

2.89 

5-440 

2.506 

Total   .    .    . 

lOO.OOO 

100.000 

IOO.OOO 

IOO.OO 

100.000 

100.000 

§  16  FUELS  63 

Under  ordinary  conditions,  a  ton  of  such  coal  should 
produce  about  10,000  cubic  feet  of  gas  of  17  candlepower; 
1,400  pounds  of  coke,  12  gallons  of  tar,  and  4  pounds  of 
ammonia. 

104.  The  following  may  be  considered  as  the  average 
composition  of  purified  coal  gas: 

PER  CENT. 

Hydrocarbon  vapors .6 

>  Heavy  hydrocarbons 4.4 

Carbon  dioxide,  CO, 3.4 

Carbon  monoxide,  CO      10.1 

Marsh  gas,  CH. 30.6 

Oxygen,  O .    .  .3 

Hydrogen,  H 45.9 

Nitrogen,  N 4.7 

Total  100X) 


WATER  GAS 

105.  Water  gas  is  a  mixture  of  hydrogen  and  carbon 
monoxide.  It  is  manufactured  commercially  by  the  contact 
of  steam  with  incandescent  carbon,  in  the  form  of  anthracite 
or  coke  which  decomposes  the  steam,  the  hydrogen  being 
separated  from  the  oxygen.  The  oxygen  takes  up  carbon 
from  the  coal  or  coke  and  forms  carbon  monoxide,  along 
with  a  small  amount  of  carbon  dioxide.  The  resultant  gases 
therefore  are  mainly  hydrogen  and  carbon  monoxide  mechan- 
ically mixed  together.  This  is  what  is  called  blue,  or 
uncarbureted,  water  gas.  It  burns  with  a  non-luminous 
flame  and  is  consequently  useless  for  lighting  purposes, 
except  in  incandescent  lamps  of  the  Welsbach  type.  In 
actual  practice,  this  water  gas  is  always  enriched  with  oil 
gas,  which  furnishes  the  hydrocarbons  necessary  to  make  a 
luminous  flame.  The  oil  gas  was  made  separately  in  many 
of  the  older  forms  of  apparatus,  but  it  is  now  commonly 
produced  in  the  same  apparatus  in  which  the  water  gas  is 
made. 


64  FUELS  §16 

106.  Impurities  in  Water  Gas. — The  only  impurity 
that  must  be  removed  from  water  gas  is  hydrogen  sulphide, 
which  is  formed  from  the   sulphur  that  is  always  present 
in  varying  amounts  in  the  coal  or  coke  and  sometimes  in  the 
oil.     The  hydrogen  sulphide  is  removed  by  purification  with 
lime  or  iron  oxide  in  the  same  way  that  the  purification  of 
coal  gas  is  accomplished. 

Carbon  dioxide,  which  is  formed  either  by  imperfect  con- 
tact of  the  steam  with  the  incandescent  carbon,  or  because 
the  temperature  of  the  carbon  is  too  low,  is  not  a  dangerous 
impurity,  but  is  merely  an  inert  gas  incapable  of  combustion. 
It,  however,  absorbs  heat  when  the  gas  is  burned,  and  is 
consequently  injurious  to  the  heating  and  lighting  power.  It 
can  be  removed  by  purification  with  lime,  but  this  is  not  neces- 
sary if  the  generating  apparatus  is  handled  properly,  as  the 
quantity  made  will  be  very  small.  No  ammonia  is  produced. 

107.  Composition    of    Purified    Water    Gas. — The 

following  is  a  volumetric  analysis  of  a  sample  of  purified 

water  gas: 

PER  CENT. 

Hydrocarbon  vapors      1.2 

Heavy  hydrocarbons 12.6 

Carbon  dioxide,  CO,  . 3.0 

Carbon  monoxide,  CO 28.0 

Marsh  gas,  CH* 20.2 

Oxygen,  O .4 

Hydrogen,  H .  31.4 

Nitrogen,  N 3.2 

Total 100.0 

108.  Water  gas  requires  from  30  to  40  pounds  of  coal 
or  coke  per  1,000  cubic  feet  of  gas  made,  and  from  4  to  5 
gallons    of   oil,    depending    on    the    candlepower    required. 
Usually  between  5  and  6  candlepower  is  obtained  from  each 
gallon  of  oil  used.     The  specific  gravity  of  24-candlepower 
water  gas  is  about  .625,  air  being  taken  as  unity. 

Pure  uncarbureted  water  gas  has  no  perceptible  odor,  but 
the  carbureted  gas  has  an  odor  fully  as  strong  as  coal  gas. 


§16 


FUELS 


65 


66  FUELS  §  16 

This  is  mainly  due  to  the  hydrocarbons  from  the  oil  that  is 
used  for  enriching. 

109.  A  good  example  of  a  water-gas  plant  is  given  in 
Fig.  12.     The  generator  a  is  first  filled,  to  the  height  shown 
in  the  figure,  with  clean  anthracite,  egg  size.     The  coal  is 
fed  through  p  from  the  second  floor,   where  it  is  stored. 
The  coal  in  the  generator  is  ignited  and  raised  to  a  very 
high  temperature  by  means  of  an  air  blast.     The  gases,  pass- 
ing through  the  pipe  /  in  the  direction  of  the  arrows,  again 
meet  with  an  air  blast  at  g,  which  blows  them  in  a  hot  flame 
through  the  superheater  /  and  out  through  the  valve  h  to  the 
smokestack.     The  body  of  the  superheater  is  filled  with  loose 
firebricks,  which  take  up  the  heat  from  the  passing  gases. 

As  soon  as  the  bricks  become  sufficiently  heated,  the  air 
blast  is  shut  off,  the  valve  h  is  closed,  and  steam  at  a  very 
high  temperature  admitted  through  the  pipe  e.  The  steam, 
on  coming  in  contact  with  the  white-hot  coal,  gives  up  its 
oxygen  which  combines  with  the  carbon  of  the  coal  to  form 
carbon  monoxide;  the  hydrogen  of  the  steam  is  set  free,  and, 
mixing  with  the  carbon  monoxide,  forms  water  gas.  This 
gas  passes  through  the  superheater,  where  any  steam 
remaining  is  further  broken  up,  and  flowing  out  through  n 
passes  through  the  washer  to  the  scrubber  y  and  thence  to  the 
condensing  apparatus. 

110.  The  water  gas,  as  it  now  is,  burns  with  a  pale-blue 
flame,  giving  little  or  no  light.     On  this  account,  it  is  neces- 
sary, in  order  to  make  the  gas  a  good  light  giver,  to  add 
some  hydrocarbon.     For  this  purpose,  oil  is  allowed  to  flow 
in  a  fine  stream  into  the  generator  from  the  reservoir  m, 
during  the  passage  of  the  steam.     These  hydrocarbons  make 
the  gas  flame  white,  and  water  gas,  properly  treated  in  this 
way,    gives    a   much   brighter   flame    than   coal    gas.     The 
hydrocarbons  are  often  added  after  the  gas  is  purified;  they 
are  not  needed,  however,  when  the  gas  is  to  be  used  for 
heating  purposes  or  for  gas  engines. 


§  16  FUELS  67 

USES  OF  GASEOUS  FUEL 

111.  Whenever  natural  gas  can  be  obtained  cheaply,  it 
is  an  ideal  fuel  for  all  heating  purposes,  and  it  is  also  most 
valuable  for  use  in  gas  engines.     Having  the  highest  fuel 
value  per  cubic  foot  of  any  of  the  mixed  gases,  it  requires 
smaller  pipes  than  any  other  for  conveying  a  quantity  having 
a  given  heating  value.     It  may  also  be  burned  in  furnaces 
for /metallurgical  purposes,  giving  a  high  temperature  with- 
out any  preheating  of  the  gas  or  air.     For  very  high  tem- 
peratures the  air  should  be  heated. 

Producer  gases  of  various  kinds,  and  water  gas,  are  used 
in  heating  furnaces,  but  in  order  to  produce  a  high  tempera- 
ture with  them,  such  as  that  required  for  melting  steel,  it  is 
necessary  to  heat  both  the  gas  and  the  air  in  a  regenerator 
before  they  are  admitted  into  the  furnace. 

The  waste  gases  of  blast  furnaces  are  burned  under  steam 
boilers  without  preheating  the  air  or  the  gas,  but  the  gas  is 
usually  delivered  from  the  furnace  at  a  temperature  of  from 
400°  to  600°  F.  They  are  also  burned  in  ovens  for  heating 
the  air  supply  of  the  blast  furnace,  and  recently  they  have 
been  used  to  some  extent  in  large  gas  engines. 

112.  Distribution    of    Gaseous    Fuel.— The   use    of 
gaseous  fuel  made  in  producers,   instead  of  solid  fuel,  is 
especially  advantageous  in  iron  and  steel  works,  where  it  is 
convenient  to  have  one  large  central  gas-producing  plant 
operated  with  a  minimum  of  labor,  and  to  distribute  the  gas 
over  moderate  distances  through  pipes  to  the   several  fur- 
naces, to  be  used  as  desired.     In  such  plants,  however,  it 
has  not  been  found  profitable  to  use  producer  gas  under 
steam  boilers,  chiefly  for  the  reason  that  there  is  a  certain 
waste  of  fuel  and  of  heat  in  making  the  gas  and  conveying 
it  to  the  boilers.     This  loss  is  saved  by  burning  the  coal 
directly  under  the  boilers. 

113.  It  has  often  been  suggested  that  it  would  be  eco- 
nomical to  have  large  central  stations  in  cities  in  which  fuel 
gas  would  be  produced  from  coal,  to  be  distributed  in  pipes 


68  FUELS  §  16 

for  domestic  use,  and  many  ventures  have  been  made  in  this 
direction,  but  they  have  all  proved  commercial  failures.  In 
order  to  be  profitable,  the  gas  would  have  to  be  sold  at  the 
works  at  a  much  higher  price  than  the  coal  from  which  it  is 
made,  and  the  cost  of  storage  and  distribution  of  producer 
gas  to  meet  a  varying  demand  is  usually  much  greater  than 
that  of  storing  and  carrying  coal. 

114.  In    connection    with    the    by-product    process    of 
coking,  there  is  a  large  amount  of  gas  given  off  and  this 
gas  is  used  for  fuel  purposes  about  the  steel  plants,  at  which 
many  of  the  by-product  coking  plants  are  located,  or  the 
gas  is  enriched  and  used  for  lighting  and  general  fuel  pur- 
poses as  is  done  at  the  plant  of  the  New  England  Gas  and 
Coke  Company  at  Everett,  near  Boston,  Massachusetts. 

115.  Use  of  Gas  in   Gas   Engines. — Whenever  it  is 
possible  to  obtain  a  given  number  of  heat  units  from  gas, 
cheaper  than  they  can  be  obtained  from -coal,  as  in  the  case 
of  the  use  of  blast-furnace  gas,  or  the  waste  gases  from 
retort  coke  ovens,  or  natural  gas  when  it  can  be  obtained 
cheaply,    it   becomes    cheaper   to    obtain    power    from    gas 
engines  than  from  steam  engines  and  boilers  using  coal. 
It  is  even  possible  to  obtain  a  given  horsepower  from  a  gas 
engine  using  gas  made  in  a  producer  from  anthracite,  with  a 
less  expenditure  of  coal  than  would  be  required  for  the  same 
power  by  a  steam  boiler  and  steam   engine.     Of  the  total 
heating  value  of  coal,  only  about  5  per  cent,  is  utilized  in 
the   shape  of  mechanical  energy  by  small  ordinary  steam 
engines,  and  less  than  16  per  cent,  by  a  triple-  or  quadruple- 
expansion  engine  of  the  best  type;  while  in  a  gas  engine  using 
gas  made  from  anthracite  or  coke,  from  12  to  20  per  cent, 
of  the  heating  value  of  the  coal  may  be  utilized.     The  best 
result  yet  obtained  from  a  steam  engine  of  the  highest  grade 
is  1  horsepower  per  hour  from  1.05  pounds  of  the  best  steam 
coal,   while  the  best  results   from   gas  producers  and  gas 
engines  are  from  .85  to  1  pound  pf  coal  per  horsepower-hour. 

116.  The  special  fields  of  the  gas  engine  are  in  localities 
where  gaseous  fuel  can  be  obtained  cheaply,  either  natural 


§16  FUELS  69 

gas,  or  waste  gas  from  furnaces  or  coke  ovens;  or  for  small 
powers,  50  horsepower  or  less,  using  illuminating  gas,  the 
extra  cost  of  fuel  being  offset  by  the  saving  of  labor  of  oper- 
ating a  steam  boiler.  The  gas  engine  is  also  well  adapted 
for  occasional  or  intermittent  service,  since  it  can  be  started 
instantly,  without  the  delay  of  getting  up  steam  in  a  boiler. 


COMBUSTION   OF  FUEL 

117.  Chemistry  of  Combustion. — In  burning  fuel  in  a 
furnace,  any  of  the  following  reactions  may  take  place,  accord- 
ing to  whether  hydrogen  or  moisture  is  present  in  the  fuel, 
and  according  to  the  conditions  under  which  air  is  supplied. 

(a)  Hydrogen  combines  with  oxygen,  forming  water,  the 
reaction  being  expressed  by  the  formula, 

2H+0  =  H,0 

2  +  16  =  18  parts  by  weight 
giving  62,000  B.  T.  U.  per  pound  of  hydrogen  burned. 

(b)  Carbon  unites  with  oxygen,  forming  carbon  monoxide, 

C+  O  =  CO 

12  +  16  =  28  parts  by  weight 
giving  4,450  B.  T.  U.  per  pound  of  carbon  burned. 

(c)  Carbon  unites  with  oxygen,  forming  carbon  dioxide, 

C+2<9  =  CO, 

12  +  32  =  44  parts  by  weight 
giving  14,600  B.  T.  U.  per  pound  of  carbon  burned. 

(d)  Carbon  unites  with   oxygen,  forming   a  mixture  of 
carbon  monoxide  and  carbon  dioxide,  according  to  the  amount 
of  oxygen  present, 

nC  +  mO  =  jiCO  +  yCO, 

(e)  If  both  hydrogen  and  carbon  are  present  in  a  fuel  as 
marsh  gas,  C//4,  and  the  supply  of  oxygen  is  ample,  the  marsh 
gas  burns  according  to  the  following  reaction, 

CM*  +  40  =  CO,  +  2N,O 

16  +  64  =  44  +  36 

giving  23,513  B.  T.  U.  per  pound  of  marsh  gas,  CV/4,  burned. 

If  the  supply  of  oxygen  is  deficient,  the  temperature  being 

moderately  low,  the  hydrogen  burns  first,  part  of  the  carbon 


70  FUELS  §  16 

escaping  as  smoke  or  soot.  With  a  greatly  deficient  supply 
of  air,  part  of  the  hydrogen  may  also  escape  unburnt,  the 
furnace  then  becoming  a  gas  producer.  The  burning  of  the 
hydrogen  alone,  leaving  all  the  carbon  unburnt,  is  expressed 
by  the  formula, 

CHt  +  2O  -=  2/fa<9  (steam)  +  C  (soot) 
12  +  4  +  32  =  86+12  parts  by  weight 
(/)     If  the  temperature  of  the  furnace  be  previously  made 
high,  however,   by  burning  carbon  to  carbon  dioxide,   and 
steam  be  injected  into  the  white-hot  coke  remaining  in  it,  the 
above  reaction  may.be  practically  reversed,  giving  at  a  very 
high  temperature  and  a  partial  supply  of  steam, 
C+H,O  -  CO  +  2H 

12  +  18  =  28  +  2  parts  by  weight 

or  a  mixture  of  carbon  monoxide  and  hydrogen,  which  is 
water  gas. 

ig)  If  the  steam  supply  be  greater,  and  the  temperature 
lower,  the  reaction  may  be 

C+2H30  =  CO.  +  1H 

12  +  36  =  44  +  4  parts  by  weight 
or  carbon  dioxide  and  hydrogen. 

118.  The  last  two  reactions  (/)  and  (g)  may  be  called 
tmburning;  they  take  as  much  heat  from  the  furnace  as  the 
burning  of  the  same  weight  of  hydrogen  to  water,  H^O,  would 
generate,  less  the  heat  that  is  made  by  burning  the  carbon. 
This  heat  production  and  absorption  may  be  computed  as 
follows: 

In  equation  (/),  the  heat  produced  in  burning  12  pounds 
of  carbon  to  carbon  monoxide  is  12  X  4,450  =  53,400  B.  T.  U. 

The  heat  absorbed  in  setting  free  2  pounds  of  hydrogen  is 
2  X  62,000  =  124,000  B.  T.  U. 

Net  absorption  of  heat  is  124,000  -  53,400  =  70,600  B.  T.  U. 

In  equation  (g),  the  heat  produced  by  burning  12  pounds 
of  carbon  to  carbon  dioxide  is  12  X  14,600  =  175,200  B.  T.  U. 

The  heat  absorbed  in  setting  free  4  pounds  of  hydrogen  is 
4  X  62,000  =  248,000  B.  T.  U. 

The  net  absorption  is  248,000  -  175,200  =  72,800  B.  T.  U. 


§  16  FUELS  71 

119.  If  air  be  blown  in  at  the  bottom  of  a  deep  bed  of 
hot  coal,  two  reactions  take  place: 

(a)  The  oxygen  supplied  by  the  air  to  the  bottom  layers 
of  coal  is  sufficient  to  burn  the  carbon  to  carbon  dioxide 
according  to  the  reaction, 

C+0,  =  CO, 

12  +  32  =  44  parts  by  weight 

producing  14,600  B.  T.  U.  per  pound  of  carbon  burned. 
(A)  The  carbon  dioxide  passing  through  the  upper  layers  of 
coal  is  reduced  to  carbon  monoxide  by  taking  up.  an  equal 
weight  of  carbon  to  that  burned  in  the  previous  reaction, 
according  to  the  reaction, 

CO,  +  C  =  2CO 
44  +  12  =  56  parts  by  weight 

and  in  so  doing  absorbing  14,600  —  4,450  =  10,150  B.  T.  U. 
per  pound  of  carbon  burned.  The  combined  result  of  these 
two  reactions  is  as  follows: 

B.T.U. 
Heat  produced  burning  1  pound  of  carbon  to  carbon 

dioxide 14,600 

Heat  absorbed  reducing  the  carbon  dioxide  to  car- 
bon monoxide  (14,600  -  4,450)    10,150 

Net  heat  produced 4,450 

Heat  produced  burning  1  pound  of  carbon  to  carbon 

monoxide 4,450 

Total  heat  produced  burning  2  pounds  of  carbon 

to  carbon  monoxide 8,900 

or,          ^|-  =  4,450  B.  T.  U.  per  pound  of  carbon 

Since  the  final  product  is  carbon  monoxide,  CO,  the  total 
net  heat  produced  by  the  combined  reactions  is  the  same 
per  pound  of  carbon  as  when  carbon  is  burned  to  carbon 
monoxide. 

EXAMPLE.— What  is  the  amount  of  heat  produced  by  the  combus- 
tion of  a  pound  of  coal  whose  analysis  is:  carbon,  86  percent.;  hydro- 
gen, 5  per  cent.;  oxygen,  8  per  cent.;  nitrogen,  1  per  cent.;  if  all  the 
available  hydrogen  is  burned,  three-fourths  of  the  carbon  is  burned 
to  carbon  dioxide,  and  one-fourth  to  carbon  monoxide? 
1  16  -27 


72  FUELS  §  16 

SOLUTION.—  The  available  hydrogen  is  5  -  f  =  4  per  cent. 
Heat  produced  per  pound  of  fuel  burned  is  as  follows: 

B.  T.  U. 
For  hydrogen,  .04  X  62,000  ............         2,480 

For    carbon    burned    to    carbon    dioxide,    f(.86) 

X  14,600  ....................         9,417 

For    carbon    burned   to   carbon   monoxide,   i(.86) 

X  4,450    ....................      _  956 

Total  heat  due  to  carbon  burned  ........       10,373 

Total  heat  produced    .    .    .    .    v   .........       12,853 

Ans. 

120.  Weight  and  Volume  of   Gases.—  Table  XXIII 
gives  the  weight  and  volume  of  the  various  gases  that  enter 
into  problems  relating    to    combustion  when   measured    at 
32°  F.  and  mean  atmospheric  pressure  at  sea  level,  which  is 
14.7  pounds  per  square  inch. 

121.  To  find  the  volume  at  any  other  temperature  and 
pressure,  the  following  formula  is  used, 


in  which  vt  =  volume  corresponding  to  the  absolute  pressure 
p*  and  the  absolute  temperature  T,  (or 
460  +  /,); 

pt  =  any  given  absolute  pressure  (for  the  figures  in 
Table  XXIII  it  is  14.7  pounds  per  square 
inch); 

vt  =  volume  at  any  other  pressure  p,  and  absolute 
temperature  71,  (or  460  +  /,). 

EXAMPLE.  —  What  is  the  volume  of  4  pounds  of  dry  air  at  75°  F. 
and  under  an  absolute  pressure  of  20  pounds  per  square  inch? 

SOLUTION.—  From  Table  XXIII,  it  is  found  that  1  Ib.  of  air,  at 
32°  F.  and  14.7  Ib.  per  sq.  in.  absolute  pressure,  occupies  12.388  cu.  ft., 
hence,  under  the  same  conditions,  4  Ib.  occupies  4  X  12.388  =  49.552 
cu.  ft.  Substituting,  in  the  formula,  the  values  va  =  49.552,  pa  =  14.7  Ib. 
per  sq.  in.,  />,  =  20  Ib.  per  sq.  in.,  /,  =  75°  F.,  we  get 

vt  =  49.552  X  —j-  X  H  =  39.6  cu.  ft.    Ans. 

122.  Fuel  Burned  In  Air.  —  In  the  preceding  state- 
ments, the  fuel  was  considered  to  be  burned  by  oxygen  gas. 


§16 


FUELS 


73 


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I&J 

o 


fOOOOOOO 
M      IH      O\>-<      txlN.Tj- 


O     O\    if)  00    00     N 

oo  oo    o    tx  ix   N 

o    o    o    o    o    1-1 


n-  oo    01  oo    o 

O     O     O     M     O 


O     O     rj-<r>i-' 


TI-COO    woo    O    rx 

rtvo    o    MVO    moo 
o\C5    o    ONCNON 


•°.g   a 


« 


74  FUELS  §  16 

In  burning  with  air,  the  chemical  reactions  are  the  same,  for 
the  nitrogen  in  the  air  passes  through  the  furnace  unchanged. 
In  calculations  of  temperature,  however,  account  must  be 
taken  of  the  nitrogen,  since  it  is  heated  by  the  combustion 
and  therefore  absorbs  heat  and  causes  the  furnace  to  have  a 
lower  temperature  than  if  oxygen  alone  were  used. 

123.  Properties  of  Air. — Pure  dry  air  is  composed  of 
a  mixture  of  20.91  parts  of  oxygen  and  79.09  parts  of  nitro- 
gen, by  volume,  or  23.15  parts  of  oxygen  and  76.85  parts  of 
nitrogen,  by  weight. 

The  approximate  proportions  usually  given  in  textbooks 
are:  by  volume,  21  parts  of  oxygen  and  79  parts  of  nitrogen; 
and  by  weight,  23  parts  of  oxygen  and  77  parts  of  nitrogen. 

The  proportion  of  nitrogen  to  oxygen  by  weight  is  76.85 
-r-  23.15  =  3.320;  by  volume,  79.09  -=-  20.91  =  3.782. 

The  proportion  of  air  to  oxygen,  by  weight,  is  100  -f-  23.15 
=  4.320;  by  volume,  100  4-  20.91  =  4.782. 

Ordinary  atmospheric  air,  outdoors,  contains  about  4  parts 
in  10,000  of  carbon  dioxide,  and  a  quantity  of  vapor  of  water 
depending  on  the  temperature  and  the  relative  humidity  of 
the  atmosphere.  The  relative  humidity  of  the  air  at  any 
time  is  the  percentage  of  moisture  contained  in  it  as  com- 
pared with  the  amount  that  it  is  capable  of  holding  at  the 
same  temperature. 

124.  Table  XXIV  gives  the  weights  of  air,  water  vapor, 
and  saturated  mixtures  of  air  and  water  vapor  at  different 
temperatures,  under  the  ordinary  atmospheric  pressure  of 
14.7  pounds  per  square  inch,  or  29.92  inches  of  mercury. 

EXAMPLE  1.— A  coal  whose  heating  value  is  12,000  B.  T.  U.  per 
pound,  is  burned  with  20  pounds  of  air  (not  including  water  vapor) 
per  pound  of  coal.  The  relative  humidity  of  the  air  is  90  per  cent.,  and 
its  temperature  is  92°  F.  How  much  heat  is  lost  in  the  chimney  gases 
on  account  of  the  moisture  in  the  air,  if  the  chimney  gases  escape 
at  512°  P.? 

SOLUTION.— From  Table  XXIV,  it  is  found  that  1  Ib.  of  air  will 
hold,  when  fully  saturated,  .03289  Ib.  of  water  vapor  at  92°  F.;  hence, 
20  Ib.  of  air  will  hold  20  X  .03289  =  .6578  Ib.  of  water  vapor;  at  90  per 
cent,  relative  humidity,  it  will  hold  .6578  X  .90  =  .59202  Ib.  water  vapor. 


§16 


FUELS 


75 


The  amount  of  heat  absorbed  in  heating  1  Ib.  of  water  from  92°  F. 
to  512°  F.  is:  (a)  From  92°  to  212°,  or  through  120°,  is  120  X  1  (specific 
heat  of  water)  =  120  B.  T.  U.;  (t>)  from  212°  to  512°,  or  through  300°, 
is  300  X  .48  (specific  heat  of  superheated  steam)  =  144  B.  T.  U.  The 
total  absorption  is  120  +  144  •=  264  B.  T.  U.  .59202  Ib.  water  will 

TABLE    XXIV 


|i 

*  * 

Mixtures  of  Air  Saturated  With  Vapor 

£ 

PS 

£  1 

I? 

£  ^5 

ssg-i 

«<%  § 

0.    S 

§|S 

Elastic 
Force  of 
Air  in 

Weight  of  Cubic  Foot  of  Mixture 
of  Air  and  Water  Vapor 

Weight 
of  Vapor 
Mixed 

$ 

•g  ^S  £ 

se« 

1  1 

Mixture 
of  Air  and 
Vapor 

Weight 
of  Air 

Weight 
of  Vapor 

Total 
Weight  of 
Mixture 

With  i 
Pound 
of  Air 

|0. 

5 

Mercury 

Pounds 

Pounds 

Pounds 

Pounds 

o 

.0864 

.044 

29.877 

.0863 

.000079 

.086379 

.00092 

12 

.0842 

.074 

29.849 

.0840 

.000130 

.084130 

•00155 

22 

.0824 

.118 

29.803 

.0821 

.OOO2O2 

.082302 

•00245 

32 

.0807 

.181 

29.740 

.0802 

.000304 

.080504 

.00379 

42 

.0791 

.267 

29.654 

.0784 

.000440 

.078840 

.00561 

52 

.0776 

.388 

29-533 

.0766 

.000627 

.077227 

.00819 

62 

.0761 

.556 

29-365 

•0747 

.000881 

•075581 

.01179 

72 

.0747 

•785 

29.136 

.0727 

.OOI22I 

.073921 

.01680 

82 

.0733 

1.092 

28.829 

.0706 

.001667 

.072267 

.02361 

92 

.0720 

1.501 

28.420 

.0684 

.OO225O 

.070717 

.03289 

IO2 

.0707 

2.036 

27.885 

.0659 

.OO2997 

.068897 

•04547 

112 

.0694 

2.731 

27.190 

.0631 

.003946 

.067046 

•06253 

122 

.0682 

3.621 

26.300 

•0599 

.005142 

.065042 

.08584 

132 

.0671 

4-752 

25.169 

•0564 

.006639 

.063039 

.11771 

142 

.0660 

6.165 

23.756 

.0524 

.008473 

.060873 

.16170 

152 

.0649 

7-930 

21.991 

•0477 

.010716 

.058416 

•22465 

162 

.0638 

10.099 

19.822 

.0423 

.013415 

•055715 

•3I7I3 

172 

.0628 

12.758 

17.163 

.0360 

.016682 

.052682 

•46338 

182 

.0618 

15-960 

I3.96I 

.0288 

.020536 

.049336 

.71300 

192 

.0609 

19.828 

10.093 

.0205 

.025142 

.045642 

>  1.22643 

2O2 

.0600 

24.450 

5-471 

.0109 

.030545 

.041445 

2.80230 

212 

.0591 

29.921 

o.ooo 

.OOOO 

.036820 

.036820 

Infinite 

absorb  264  X  .59202  =  156.29  B.  T.  U.,  or  - 
of  the  heating  value  pf  the  coal.     Ans. 

EXAMPLE  2. — How  many  cubic  feet  of  dry  air  per  pound  of  coal  are 
used  in  the  case  of  example  1,  if  the  air  is  at  the  mean  atmospheric 
pressure  of  14.7  pounds  per  square  inch? 


76 


FUELS 


§16 


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SOLUTION.— From  the 
Table  XXIV,  by  calcula- 
tion, it  is  found  that  1  Ib.  of 
air  at  32°  and  at  the  mean 
atmospheric  pressure  oc- 
cupies -^  =  12.39  cu. 

ft.     At   92°  it   occupies 
92  +  460 


12.39  X  ^7^ 


13.9 


492 

cu.  ft.;  20  Ib.  will  occupy 
13.9  X  20  =  278  cu.  ft. 

Ans. 

EXAMPLE  3.  — How 
many  cubic  feet  of  air 
must  be  delivered  per 
minute  by  a  fan,  to  drive 
1,000  horsepower  of  boil- 
ers under  the  conditions 
of  examples  1  and  2,  if 
4  pounds  of  coal  is  burned 
per  horsepower-hour? 

SOLUTION. — 

4  X  1,000  X  278 

— gg —          =  18,533 

cu.  ft.  per  minute.     Ans. 

125.  Quantity 
of  Air  Required 
for  Combustion. 

Table  XXV  shows  the 
chemical  reactions  in- 
volved in  the  com- 
bustion of  hydrogen, 
carbon,  and  sulphur, 
the  weights  of  oxygen 
required  per  pound 
of  fuel,  of  the  nitro- 
gen mixed  with  the 
air,  of  the  air,  and 
of  the  gaseous  prod- 
ucts. 


§  16  FUELS  77 

126.  It  is  found,  in  practice,  that  if  air  is  blown  through 
a  bed  of  hot  anthracite  or  coke,  and  the  resulting  gases  are 
analyzed,  they  always  contain  some  carbon  monoxide,  show- 
ing imperfect  combustion,  unless  they  contain  a  considerable 
quantity  of  uncombined  oxygen,  or  air.  The  excess  of  air 
required  to  effect  complete  combustion  to  carbon  dioxide  is 
usually  not  less  than  50  per  cent,  of  that  theoretically 
necessary,  so  that  about  17  pounds  of  air  is  required  to 
insure  the  complete  combustion  of  1  pound  of  carbon  instead 
of  '11.52  pounds,  the  figure  given  in  Table  XXV.  It  is 
probable,  also,  that  more  than  34.56  pounds  of  air  is 
required  to  effect  the  combustion  of  each  pound  of  hydro- 
gen in  a  furnace,  although,  experimentally,  one  volume  of 
oxygen  and  two  volumes  of  hydrogen  mixed  together,  or 
eight  parts  by  weight  of  oxygen  to  one  of  hydrogen  may  be 
exploded  by  a  spark,  and  converted  into  water  vapor.  The 
excess  of  air  required  in  furnaces  may  be  due  to  the  pres- 
ence of  the  great  volume  of  nitrogen  and  carbon  dioxide, 
which  dilute  the  oxygen  and  make  it  less  active  in  causing 
combustion. 

EXAMPLE:  1. — How  much  air  is  required  for  the  complete  combustion 
of  1  pound  of  coal  containing  5  per  cent,  moisture,  20  per  cent,  volatile 
matter,  60  per  cent,  fixed  carbon,  15  per  cent,  ash,  assuming  the  vola- 
tile matter  to  be  of  the  composition  of  marsh  gas  (methane),  CHJ 

SOLUTION. — The  molecular  weight  of  marsh  gas  is  12  +  4  =  16; 
hence,  three-fourths  of  the  weight  of  the  volatile  matter  is  carbon  and 
one-fourth  hydrogen.  The  carbon  of  the  volatile  matter  is  f  X  20 
=  15  per  cent,  of  the  fuel.  The  fixed  carbon  is  given  as  60  per  cent. 
The  total  carbon  is  15  +  60  =  75  per  cent.  The  hydrogen  of  the  vola- 
tile matter  is  i  X  20  =  5  per  cent,  of  the  fuel. 

Since  from  Table  XXV,  11.52  Ib.  of  air  is  required  to  burn  1  Ib.  of 
carbon  to  CO,,  and  34.56  Ib.  of  air  is  required  to  burn  1  Ib.  of  hydro- 
gen, the  theoretical  amount  of  air  required  to  burn  the  fuel  will  be: 

POUNDS 

For  the  carbon  .75  X  11.52 8.640 

For  the  hydrogen  .05  X  34.56 1.728 

Total 10.368    Ans. 

If  an  excess  of  50  per  cent,  of  air  be  allowed,  the  amount  will  be 
1.5  X  10.368  =  15.552  Ib.  Ans. 


78 


FUELS 


EXAMPLE  2. — How  many  cubic  feet  of  dry  air  at  62°  F.  will  be 
required  in  example  1? 

SOLUTION.— The  weight  of  1  cu.  ft.  of  air  at  a  temperature  of  62°  F. 
and  a  barometric  pressure  of  29.92  is  .0761  lb.;  hence,  10.368  lb. 

=  1M§§  =  136.24  cu.  ft.  and  15.552  lb.  =  ~,?Jr  =  204.36  cu.  ft.  Ans. 
.0/61  .U/bi 

127.  Temperature  of  Ignition. — Every  combustible 
must  be  heated  to  a  certain  temperature,  known  as  the 
temperature  of  ignition,  or  kindling  point,  before  it  will  com- 
bine, with  oxygen,  or  burn.  Table  XXVI  gives  the  tempera- 
tures of  ignition  of  various  fuels  as  determined  by  different 
authorities. 

TABLE   XXVI 


Fuel 

Temperature  of 
Ignition 
Degrees  F. 

Marsh  gas  (methane)    CH± 

I   2O2* 

Carbon  monoxide,  CO    .... 

1,202  tO   1,21  1 

Carbon  monoxide,  CO,  in  presence  of  a  large 
quantity  of  carbon  dioxide  CO  
Ethylene  (olefiant  gas),  Ca//4  
Hydrogen          ... 

1,292 
I.O22 

1,031  to  1,130 

Anthracite 

02  ^ 

Semibituminous  coal 

870 

Bituminous  coal  
Cannel  coal 

766 

668 

Soft  charcoal,  prepared  at  500°  F  
Sulphur      

650 
470 

It  appears  from  Table  XXVI  that  it  requires  a  consider- 
ably higher  temperature  to  ignite  the  gases  distilled  from 
coal  than  to  ignite  the  coal  itself,  the  temperature  of  ignition 
of  the  carbon  being  lower  than  that  of  ignition  of  the  gases. 


*The  temperature  of  ignition  of  marsh  gas  diluted  with  carbon 
dioxide  and  nitrogen  in  the  proportions  ordinarily  found  in  a  furnace 
is  given  by  the  French  Coal  Commission  as  1,436°  F. 


§16 


FUELS 


79 


128.  The  temperature  of  ignition  of  charcoal  varies  with 
the  temperature  at  which  the  charcoal  was  made,  the  higher 
the  temperature  of  manufacture  or  preparation,  the  higher  the 
temperature  of  ignition,  as  is  shown  in  Table  XXVII. 

129.  Temperature   of   the   Fire. — Assuming    that   a 
pure  fuel,  such  as  carbon,  is  thoroughly  burned  in  a  furnace, 
all  the  heat  generated  will  be  transferred  to  the  gaseous  prod- 
ucts of  combustion,   raising   their  temperature  above  that 
at  which  the  fuel  and  the  oxygen  or  air  are  supplied  to  the 
furnace.     Suppose  that  1  pound  of    carbon  is  burned  with 
2f  pounds  of  oxygen,  forming  3f  pounds  of  carbon  dioxide, 
both  the  carbon  and  the  oxygen  being  supplied  at  0°  F. 
The  combustion  of  the  pound  of  carbon  generates   14,600 
B.  T.  U.,  which  will  all  be  contained  in  the  3f  pounds  of  car- 
bon dioxide.     The  specific  heat  of  carbon  dioxide  is  .217  at 
constant  pressure;  that  is,  it  requires  .217  B.  T.  U.  to  raise 

TABLE  XXVII 


Degrees 

Degrees 

Degrees 

Degrees 

Degrees 

Temperature  of  preparatioh 
Temperature  of  ignition     . 

1,000 

800 

1,500 
900 

2,000 
I,  TOO 

2,500 
1,300 

3,000 
2,500 

the  temperature  of  1  pound  of  carbon  dioxide,  1°  F.  To 
raise  3|  pounds  of  carbon  dioxide  1°  F.  will  require  3fx.217 
=  .7957  B.T.U.,  and  14,600  B.T.U.  will  therefore  raise  its 
temperature  14,600  -=-  .7957  =  18,348.6°  F.  (approximately 
18,350°  F.)  above  the  temperature  at  which  the  carbon  and 
the  oxygen  were  supplied.  The  temperatures  thus  calcu- 
lated are  known  as  theoretical  temperatures,  and  are  based 
on  the  assumptions  of  perfect  combustion  and  no  loss  by 
radiation'.  The  temperature  of  18,350°  is  far  beyond  any 
temperature  known  in  the  arts,  and  it  is  probable  that  long 
before  it  could  be  reached,  the  phenomenon  of  dissociation 
would  take  place;  that  is,  the  carbon  dioxide  would  be  split 
into  carbon  and  oxygen,  and  the  elements  would  lose  their 
affinity  for  each  other. 


80  FUELS  §  16 

130.  The  theoretical  elevation  of   temperature  of  the 
fire  may  conveniently  be  calculated  by  the  formula 

_,         .         ,  B.T.  U.  generated  by  the  combustion 

Elevation  of  temperature  =  Wej?ht  of  ?aseous  product7x'thelr  •peciflc-fae^i 

It  is  evident  from  this  formula  that  the  rapidity  of  the 
combustion,  or  the  time  required  to  burn  a  given  weight  of 
fuel,  has  nothing  to  do  with  the  temperature  that  may  theo- 
retically be  attained.  In  practice,  the  temperature  of  a  bed 
of  coal  in  a  furnace  and  that  of  the  burning  gases  immedi- 
ately above  the  coal  are  reduced,  to  some  extent,  by  radia- 
tion; and  as  the  quantity  of  heat  radiated  from  a  given  mass 
of  fuel  is  a  function  of  the  time  during  which  it  takes  place, 
a  considerable  portion  of  the  heat  generated  may  be  lost  by 
radiation  when  the  combustion  is  very  slow.  With  ordinary 
rates  of  combustion,  however,  that  is,  of  about  10  pounds  of 
coal  per  square  foot  of  grate  surface  per  hour,  and  firebrick 
furnaces,  the  percentage  of  loss  of  heat  by  radiation  is  quite 
small,  1  per  cent,  or  less,  and  the  actual  temperature  that 
may  be  attained  will  be  very  nearly  as  high  with  that  rate  of 
combustion  as  with  a  rate  of  20  or  40  pounds. 

131.  The  elevations  of   temperatures    given   in  Table 
XXVIII  were  determined  by  means  of  the  preceding  for- 
mula.    In  this  table,  the  specific  heat  of  the  chimney  gases 
is  taken  as  .24. 

132.  Maximum    Theoretical    Temperature   of   the 
Fire  Due  to  Burning  Hydrogen  In  Dry  Air. — To  burn 
1  pound  of  hydrogen,  8  pounds  of  oxygen  is  required,  and 
there  is  also  present  8  X  3.32  =  26.56  pounds  of  nitrogen, 
which  is  mixed  with  the  oxygen  in  the  air.     The  gaseous 
products  are  9  pounds  of  water,  in  the  shape  of  superheated 
steam    (specific   heat  .48),   and   26.56   pounds   of   nitrogen 
(specific  heat  .2438).     The  heat  produced  is  62,000  B.  T.  U. 
If  the  temperature  of  the  atmosphere  is  62°  F".,  150  B.  T.  U. 
is  absorbed  during  the  combustion  in  heating  1  pound  of 
water,  H,O,  from  62°  to  212°  F.  per  pound,  965.8  B.  T.  U., 
in  evaporating  it  at  that  temperature,  and  .48  (T  +  t  —  212) 
in  superheating  it  from  212°  to  the  temperature  T -\-  t  of  the 


§16 


FUELS 


81 


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82  FUELS  §  16 

fire,  T  being  the  increase  of  temperature  and  /  the  tempera- 
ture of  the  atmosphere,  which  in  this  case  is  62°  F.  All 
this  heat  may  be  recovered  by  condensing  the  steam  and 
cooling  the  water  of  condensation  to  62°.  We,  therefore, 
obtain  the  following  equation: 

62,000  =  9[150  +  965.8  +  0.48(7'+  62  -  212)] 
+  26.56  X  .2438  T 

which  being  solved  gives,  T  =  4,873°  F.  T+t  =  4,935°  F. 
Showing  that  hydrogen  and  carbon,  when  perfectly  burned, 
give  about  the  same  maximum  theoretical  temperature. 

133.  Temperature  of  the  Fire,  the  Fuel  Contain- 
ing Hydrogen  and  Water. — By  a  process  of  reasoning 
similar  to  the  preceding,  the  following  formula  is  derived, 
to  obtain  the  maximum  theoretical  temperature  of  the  fire, 
when  the  fuel  contains  hydrogen  and  moisture  with  a  varying 
supply  of  air. 

T=  616  C+  2,220^7-  327  O  -  44 H/ 
/+  .02H/  +  .18^7 

in  which  T  =  elevation  of  temperature  above  that  of  atmos- 
phere; 

C  =  percentage  of  carbon  in  fuel; 
H  —  percentage  of  hydrogen  in  fuel; 
O  =  percentage  of  oxygen  in  fuel; 
W  =  percentage  of  water  in  fuel; 
/  =  pounds    of   dry    gases    of   combustion    (ff,O 
excluded)  per  pound  of  fuel. 

EXAMPLE  1.— What  would  be  the  temperature  of  the  fire,  the  tem- 
perature of  the  atmosphere  being  62°  F.,  in  burning  a  coal  having  the 
composition,  excluding  ash  and  sulphur,  carbon  75  per  cent.,  hydro- 
gen 5  per  cent.,  oxygen  10  per  cent.,  moisture  10  per  cent.;  the  dry 
chimney  gases  amount  to  20  pounds  per  pound  of  this  combustible, 
including  the  moisture? 

SOLUTION. — Applying  the  formula, 

~  _  616  X  75  +  2,220  X  5  -  327  X  10  -  44  X  10  _  9  ,  .ft0  _, 

20 +.02X10 +.18X5  "**°* 

T+  *  =  2,540°  +  62°  =  2,602°  F.     Ans. 

EXAMPLE  2.— What  is  the  maximum  temperature  attainable  by 
burning  moist  wood  of  the  composition  carbon  38  per  cent.,  hydrogen 


§  16  FUELS  83 

5  per  cent.,  oxygen  32  per  cent.,  nitrogen  and  ash  1  per  cent.,  mois- 
ture 24  per  cent.;  the  dry  gases  are  15  pounds  per  pound  of  wood, 
and  the  temperature  of  the  atmosphere  is  62°  P.? 

SOLUTION.—  Applying  the'  formula, 

616  X  38  +  2,220  X  5  -  327  X  32  -  44  X  24 


15  +  .02  X  24  +  .18  X  5 
T  +  t  =  1,403°  +  62°  =  1,465°  F.    Ans. 


EXAMPLE:  3.—  What  will  be  the  temperature  of  a  fire  of  Pocahontas 
coal  analyzing  carbon  84.22  per  cent.,  hydrogen  4.26  per  cent., 
oxygen  3.48  per  cent.,  nitrogen  .84  per  cent.,  sulphur  .59  per  cent  , 
ash  5.85  per  cent.,  water  .76  per  cent.;  the  dry  gases  are  20  pounds 
per  pound  of  combustible,  the  heating  value  of  the  sulphur  being 
neglected? 

SOLUTION.  —  The  combustible,  carbon  and  hydrogen,  is  88.48  per 
cent,    of     the    coal,     hence   /  =  20  X  .8848  =  17.69.     Applying    the 
formula, 
T  _  616  X  84.22  +  2,220  X  4.26  -  327  X  3.48  -  44  X  .76  _  0 

17.69  +  .02  X  .76  +  .18  X  4.26  =     ' 

T+  t  =  3,257°  +  62°  =  3,319°  F.     Ans. 

134.  Actual  Temperature  Lower  Than  Theoretical  . 

When  the  combustion  is  perfect,  and  the  furnace  is  entirely 
enclosed  in  walls  of  firebrick,  highly  heated,  the  temperatures 
calculated  by  the  formula  are  nearly  attained,  the  only  loss 
being  that  due  to  external  radiation.  In  ordinary  practice, 
with  the  boiler  immediately  above  the  fire,  the  temperature 
is  lowered  by  radiation,  and  also,  when  soft  coal  is  used,  by 
imperfect  combustion. 

135.  Estimation    of    Air    Supply.  —  The    theoretical 
amounts  of  air  required  to  burn  the  several  combustible  ele- 
ments in  a  fuel  were  given  in  Table  XXV,  but  when  burning 
coal  in  a  furnace  only  a  rough  estimate  of  the  quantity  of  air 
supplied   may  be  obtained   by  direct   measurement   by  an 
anemometer,  or  by  counting  the  revolutions  of  a  fan.     If  it 
were  practicable  to  measure  the  air  in  a  large  tank  like  a 
gasometer,  or  to  pass  it  through  a  gas  meter,  a  correct  meas- 
urement might  be  obtained,  but  this  is  not  practicable  except 
in  a  laboratory  experiment.     The  best,  and,  in  fact,  the  only 
available  method  of  closely  approximating  the  amount  of  air 
supplied,  is  by  making  a  proximate  analysis  of  the  gases  of 


84  FUELS  §16 

combustion,  taken  from  a  point  close  to  the  furnace,  but 
beyond  the  point  of  visible  flame.  If  taken  from  the  chimney, 
the  gas  may  be  of  different  composition  on  account  of  inward 
leaks  of  air  through  cracks  in  the  brickwork.  The  analysis  of 
the  gases  gives  the  percentage  of  carbon  dioxide,  oxygen,  and 
carbon  monoxide,  in  this  order,  the  quantity  of  these  gases 
being  determined  by  absorption;  nitrogen  is  determined  by 
difference;  that  is,  the  remainder  after  subtracting  the  sum 
of  the  other  three  gases  from  100.  Unburned  hydrogen  or 
hydrocarbon  gases  cannot  be  conveniently  determined  by 
ordinary  analysis.  If  the  combustion  is  complete,  the  per- 
centage of  nitrogen  will  always  be  found  between  79  and  80 
per  cent.  If  it  exceeds  80  per  cent.,  it  is  evidence  either  of 
the  presence  of  unburned  hydrogen,  or  hydrocarbons,  or  of 
error  in  the  analysis,  or  possibly,  of  the  burning  of  the 
hydrogen  of  a  gaseous  fuel,  leaving  carbon  unburned. 
Thus,  in  burning  marsh  gas  (methane),  CH<,  with  an  insuffi- 
cient supply  of  air,  the  hydrogen  only  may  be  burned  to 
water,  H,O,  leaving  the  carbon  unburned  in  the  shape  of 
soot,  which  is  caught  in  a  filter  attached  to  the  gas-collecting 
apparatus.  The  water,  or  water  vapor,  is  condensed,  and 
is  not  determined  in  the  analysis,  leaving  the  nitrogen  that 
accompanied  the  oxygen,  alone  to  be  determined.  In  this 
manner,  the  nitrogen  in  the  gases  may  actually  exceed  80 
per  cent. 

136.  The  following  formula  may  be  used  for  calculating 
the  air  supply: 

3  032  JV 
Pounds  of  dry  air  per  pound  of  carbon  =  — -j —- 

in  which  CO,,  CO,  and  N  are  percentages,  by  volume,  of  the 
dry  gas. 

EXAMPLE.— How  many  pounds  of  air  are  supplied  per  pound  of 
carbon  in  burning  a  coal,  if  the  gases  analyze  carbon  dioxide  11.74  per 
cent.,  carbon  monoxide  .10  per  cent.,  oxygen  7.71  per  cent.,  nitrogen 
80.45  per  cent? 

SOLUTION. — Substituting  in  the  formula, 


§16  FUELS  85 


HEAT  OF  COMBUSTION 

137.  Every    combustible    chemical    element,    such    as 
carbon,  hydrogen,  and  sulphur,  and  every  gaseous  fuel  of 
definite  chemical  composition,  containing  two  or  more  ele- 
ments,   such    as    carbon    monoxide,    CO,    and    marsh    gas 
(methane),  CH*,  when  completely  burned  in  oxygen  or  in 
air  generates  a  definite  quantity  of  heat  per  pound  of  the 
combustible,  which  quantity  may  be  ascertained  with  a  close 
approximation  to  accuracy  by  means  of  an  instrument  known 
as    a  fuel  calorimeter,   in  which    all    the  heat  generated  is 
absorbed  in  a  weighed  quantity  of  water  and  is  measured 
by  the  rise  in  temperature  of  the  water  and  the  vessel  that 
contains  it.     The  exact  determination  of  the  heat  of  combus- 
tion, or  calorific  value,  of  any  combustible  requires  a  very 
delicate  apparatus,  a  high  degree  of  skill  on  the  part  of  the 
operator,  and  an  allowance  for  certain  unavoidable  errors, 
such  as  loss  by  radiation,  so  that  the  calorific  values  of 
different  combustibles  as  reported  by  different  authorities 
show  a  slight  variation. 

138.  Dulong's  Formula. — The  heating  value  of  any 
fuel,  such  as  coal,  consisting  of  a  mixture  of  combustible  and 
non-combustible  substances  may  be  directly  determined  by 
means  of  a  calorimeter,   or  it  may  be  calculated  from  its 
ultimate  chemical  analysis  by  Dulong's  formula,  which  is: 

Heating  value  =^X  [~14,600  C  +  62,000  ( H- %}  +  4,000  S\ 
loo    L  \       o/  J 

or,         heating  value  =  146  C  +  620  (#  -  j-\  +'  40  S 

in  which  C,  H,   O,  and  S  are  the  percentages  of  carbon, 
hydrogen,  oxygen,  and  sulphur  in  the  fuel,  as  determined 

by  ultimate  analysis.     The  available  hydrogenf//—  -J  or 

that   which   is   not    combined    with    oxygen,    is   found   as 
explained  in  Art.  4. 

139.  For  all  the  common  varieties  of  coal — cannel  coal 
and  some  lignites  excepted — the  formula  is  accurate  within 


FUELS 


§16 


the   limits    of  error  of  chemical  analysis   and  calorimetric 
determinations. 

EXAMPLE.—  What  is  the  heating  value  of  a  coal  whose  analysis  is 
moisture  5  per  cent.,  carbon  70  per  cent.,  hydrogen  5  per  cent., 
oxygen  12  per  cent.,  nitrogen  1  per  cent.,  sulphur  2  per  cent.,  ash 
5  per  cent.? 

SOLUTION.  —  Substituting  in  the  formula  given  in  Art.  138, 
146  X  70  +  620  (5  -  1.5)  +  2  X  40  =  12,470  B.  T.  U.     Ans. 

140.  Iiord  and  Haas's  Formula.  —  The  following 
formula  is  based  on  extensive  experiments  made  at  the 
Ohio  State  University  by  Messrs.  Lord  and  Haas  and  the 
results  calculated  by  it  have  been  found  to  agree  very  closely 
with  those  obtained  with  the  Mahler  calorimeter. 

-A-S  -  M)  +  (SX  4,050)          m 
100 


P  T  U  = 


in  which  the  ash  A,  sulphur  S,  and  moisture^/" are  expressed 
as  percentages,  and  A' is  a  cdnstant  determined  from  a  num- 
ber of  chemical  and  calorimetric  determinations  by  the 
following  formula,  in  which  the  values  substituted  are  the 
averages  of  a  number  of  analyses: 

K=      B.  T.  U.  -  (sulphur  X  4,050)  ^) 

100  —  (ash  -f-  sulphur  +  moisture 

141.     Table  XXIX  gives    the  average  values  of  K  as 
determined  for  different  coals  by  Lord  and  Haas. 

TABLE  XXIX 


Coal 

Value  of  K 

Upper  Freeport,  Ohio  and  Pa. 

15,1  16 

Pittsburg,  Pa. 

iq   18? 

Middle  Kittanning  (Darlington  coal),  Pa  
Middle  Kittanning  (Hocking  Valley  coal),  Ohio  . 
Thacker,  W.  Va. 

15,062 
14,265 
I  c  4  10 

Pocahontas   \V   Va 

I  ^  820 

Fairmont,  W.  Va  .    . 

I  ^  6?^ 

§  16  FUELS  87 

EXAMPLE.  —  An  average  sample  of  Fairmont,  W.  Va.,  coal  is  mois- 
ture 1.5  per  cent.,  volatile  matter  36  per  cent.,  fixed  carbon  54.8  percent., 
sulphur  2.1  per  cent.,  ash  7  per  cent.;  what  is  the  calorific  power? 

SOLUTION.—  From  Table  XXIX,  the  value  of  K  for  Fairmont  coal 
is  found  to  be  15,675.  Substituting  this  value  in  formula  1  of  Art.  14O, 


B.  T.  u^-  7  -2.1^-1.5)+  2.1X4.050  _  ^  5  B  T  ^ 

Ans. 

142.  Calculating  Heating  Value  of  a  Compound 
Gas.  —  The  heating  value  of  a  compound  or  mixed  gas  is 
generally  taken  as  the  sum  of  the  heating  values  of  its  ele- 
mentary fuel  constituents,  carbon  and  hydrogen.     The  rule 
does  not  apply  in   the  case  of   carbon   monoxide,  CO,  on 
account  of  the  partial  oxidation  of  the  carbon.    According  to 
Favre  and  Silbermann's  figures,  1  pound  of  carbon  in  carbon 
monoxide  generates  only  10,093  B.  T.  U.  in  burning  to  car- 
bon dioxide,  while  1  pound  of  carbon  burning  directly  to 
carbon  dioxide,  generates   14,544  B.  T.  U.     The  difference, 
4,451  B.  T.  U.,  is  the  heat  generated  when  the  carbon  mon- 
oxide was  formed  by  burning  carbon  with  oxygen.     It  also 
does  not  appear  to  apply  in  the  case  of  marsh  gas  (methane) 
and  other  gases. 

143.  In  making  the  calculation  of  the  heating  value  of  a 
compound  gas,  the  atomic  or  combining  weights  of  the  sev- 
eral elements  have  to  be  taken  into  account.     For  example, 
marsh    gas    (methane),  C7/4,  consists  of    twelve   parts,    by 
weight,  of  carbon  and  four  parts,  by  weight,  of  hydrogen,  or 
sixteen  parts  in  all.     To  find  the  calorific  value  of  1  pound 
of  the  gas  compute  the  calorific  value  of  12  pounds  of  car- 
bon and  4  pounds  of  hydrogen  and  divide  the  sum  of  these 

two  quantities  by  16,  thus: 

B.  T.  U. 

Calorific    value    of     12    pounds    carbon, 

12  X  14,600    ............     175,200 

Calorific    value    of    4    pounds    hydrogen, 
4X62,000  ..............     248.000 

Total  ...............     423,200 

The  calorific  value  of  1  pound  of  marsh  gas  is  423,200 
-5-  16  =  26,450  B.  T.  U. 

145—28 


88  FUELS  §  16 

The  value  obtained  by  the  calorimeter  as  given  in  Table 
XX  is  23,513  B.T.U.,  a  difference  of  2,937  B.T.U.  The 
calculated  values  of  ethylene,  CtHt,  and  of  benzole  vapor, 
C.//.,  are,  respectively,  21,370  and  18,246  B.  T.  U.,  which  are 
very  close  to  the  calorimetric  values.  This  difference  is  due 
to  the  heat  absorbed  by  the  decomposition  of  the  compound. 

144.     Heat    Absorbed    by    Decomposition. — By   the 

decomposition  of  a  chemical  compound  as  much  heat  is 
absorbed  or  rendered  latent  as  was  evolved  when  the  com- 
pound was  formed.  If  1  pound  of  carbon  is  burned  to  carbon 
dioxide,  generating  14,600  B.  T.  U.,  and  the  carbon  dioxide 
thus  formed  is  immediately  reduced  to  carbon  monoxide  by 
being  passed  through  a  body  of  glowing  carbon,  by  the  reac- 
tion CO,  +  C  =  2C6>,  the  result  is  the  same  as  if  the  2  pounds 
of  carbon  had  been  originally  burned  to  carbon  monoxide, 
generating  2  X  4,450  =  8,900  B.  T.  U.  The  2  pounds  of 
carbon  burned  to  carbon  dioxide  will  generate  2  X  14,600 
=  29,200  B.  T.  U.,  the  difference,  29,200  -  8,900  =  20,300 
B.  T.  U.,  being  absorbed  or  rendered  latent  in  the  carbon 
monoxide,  or  10,150  B.  T.  U.  for  each  pound  of  carbon. 

In  like  manner,  if  9  pounds  of  water  (which  might  be 
formed  by  burning  1  pound  of  hydrogen  with  the  generation 
of  62,000  B.  T.  U.  and  cooling  the  resulting  water  to  the 
atmospheric  temperature)  be  injected  into  a  large  bed  of 
glowing  coal,  it  will  be  decomposed  into  1  pound  of  hydro- 
gen and  8  pounds  of  oxygen.  The  decomposition  will 
absorb  62,000  B.  T.  U.,  cooling  the  bed  of  coal  this  amount, 
and  the  same  quantity  of  heat  will  again  be  evolved  if  the 
hydrogen  is  subsequently  burned  with  a  fresh  supply  of 
oxygen.  The  8  pounds  of  oxygen  will  enter  into  combina- 
tion with  6  pounds  of  carbon,  forming  14  pounds  of  carbon 
monoxide  (since  carbon  monoxide  is  composed  of  twelve 
parts  carbon  to  sixteen  parts  oxygen),  generating  6  X  4,450 
=  26,700  B.  T.  U.,  and  6  X  10,150  =  60,900  B.  T.  U.  will  be 
latent  in  this  14  pounds  of  carbon  monoxide,  to  be  evolved 
later  if  it  is  burned  to  carbon  dioxide  with  an  additional 
supply  of  8  pounds  of  oxygen. 


§  16  FUELS  89 

145.  Available  Heating  Value  of  Fuel  Containing 
Hydrogen  and  Water. — In  burning  a  fuel  containing  hydro- 
gen and  water  in  a  furnace,  some  of  the  heat  is  unavoidably 
lost  on  account  of  the  original  water  and  the  water  formed 
by  burning  the  hydrogen  escaping  into  the  chimney  in  the 
form  of  superheated  steam.  In  calculating  the  efficiency  of 
a  steam  boiler,  it  is  customary  to  charge  it  with  the  total 
heating  value  of  the  fuel  consumed  and  to  consider  the  loss 
due,  to  this  superheated  steam  as  part  of  the  several  losses  in 
the  operation  of  the  boiler,  such,  for  instance,  as  the  heating 
of  the  air  that  also  passes  through  the  furnace  and  enters  the 
chimney.  It  is  sometimes  convenient,  however,  to  compute 
the  loss  due  to  the  superheated  steam  as  a  deduction  from 
the  heating  value  of  the  fuel  itself,  and  in  such  cases  the  fol- 
lowing formula  is  used  to  obtain  the  amount  of  this  loss: 

B.  T.  U.  lost  =    (gm  +  ^)X  [(212- /)+965.8 +  .48  (T-212)] 

in  which   H  =  percentage  of  hydrogen; 

W  =  percentage  of  water  in  fuel; 
/  =  temperature  of  air  supply; 
T  =  temperature  of  chimney  gas. 

EXAMPLE. — A  coal  has  the  following  analysis:  Moisture,  5  per 
cent.;  carbon,  70  per  cent.;  hydrogen,  5  per  cent.;  oxygen,  12  per 
cent.;  nitrogen,  1  per  cent.;  sulphur,  2  per  cent.;  ash,  5  per  cent, 
(a)  What  will  be  the  loss  in  heating  power  due  to  the  presence  of  the 
hydrogen  and  moisture,  assuming  that  the  chimney  gases  escape  at  a 
temperature  of  562°  F. ,  the  temperature  of  the  atmosphere  being  62°  F.  ? 
(d)  If  the  weight  of  the  chimney  gases  is  20  pounds  per  pound  of  coal 
and  the  specific  heat  of  the  gases  is  .24,  what  is  the  loss  of  heat  due  to 
the  escape  of  the  chimney  gases?  (c)  What  is  the  total  amount  of 
heat  utilized  in  the  furnace,  assuming  that  there  is  no  loss  from 
radiation? 

SOLUTION.— (a)     Substituting  in  the  formula  in  Art.  145, 
B.  T.  U.  lost  =  (9  X  .05  +  .05)  X  [(212  -  62)  +  965.8  +  .48(562  -  212)] 
=  641.9  B.  T.  U.     Ans. 

(6)  20  X  (562  -  62)  X  .24  =  2,400  B.  T.  U.     Ans. 

(c)  From  the  formula  in  Art.  138,  the  heating  value  of  this  coal 
is  found  to  be,  146  X  70  +  620  (5  -  1.5)  +  2  X  40  =  12,470  B.  T.  U. 

The  total  heat  lost  is  641.8  +  2,400  =  3,041.8  B.  T.  U. 

The  heat  utilized  is  12,470  -  3,041.8  =  9,428.2  B.  T.  U.     Ans. 


90 


FUELS 


§16 


CALORIFIC  VALUE  OF  FUELS 

146.  When   it   is    necessary    to   determine    the    actual 
calorific  value  of  a  fuel,  it  is  done  by  means  of  an  instru- 
ment called  a  calorimeter.     Though  there  are  many  forms 
of  this  instrument,  all  are  so  constructed  that  a  weighed 
quantity  of  a  fuel  can  be  burned  in  a  vessel  submerged  in  a 
weighed  quantity  of  water,  which  absorbs  the  heat  developed. 
The  calorific  value  is  computed  from  the  rise  in  temperature 
of  the  water. 

147.  Mahler's  Bomb  Calorimeter. — The  most  accu- 
rate apparatus  for  ascertaining  the  heating  value  of  a  solid 
or  liquid  fuel  is  known  as  Mahler's  bomb  calorimeter, 
shown  in  Fig.  13.     It  consists  of  a  shell  a  of  forged  steel, 
about  6  inches  high  and  4  inches  in  diameter,  with  a  tight 


cover,  inserted  in  a  thin  brass  vessel  b  containing  water, 
and  surrounded  by  non-conducting  substances  and  by  a 
larger  annular  vessel  c  containing  water,  to  minimize  losses 
of  heat  by  radiation.  The  inner  vessel  b  contains  a  device 
for  stirring  the  water.  About  1  gram  of  the  pulverized  fuel 


§  16  FUELS  91 

whose  heating  value  is  to  be  determined  is  placed  in  a  small 
tray  d  [shown  enlarged  at  (b\\  inside  the  bomb.  The  bomb 
cover  being  tightly  closed,  the  shell  a  is  filled  with  oxygen 
at  a  pressure  of  20  to  25  atmospheres  from  the  gas  cylinder  e 
alongside.  The  temperature  of  the  water  in  the  inner  vessel  b 
is  carefully  noted  to  .01°  C.,  by  the  thermometer  /,  and  then 
the  coal  or  other  fuel  is  set  on  fire  by  means  of  an  electric 
spark  from  wires  g,g*  that  are  carried  through  gas-tight 
nipples  in  the  cover.  The  fuel  burns  instantly  with  an 
explosion,  and  the  heat  generated  is  radiated  through  the 
bomb  into  the  water  in  the  inner  vessel,  which  is  constantly 
stirred.  Observations  of  the  rise  of  temperature  are  made 
and  recorded  every  quarter  minute,  until  often  the  temperature 
has  been  considerably  reduced  by  radiation.  A  study  of  the 
temperature  record  is  then  made  to  determine  what  would  have 
been  the  maximum  temperature  if  there  had  been  no  external 
radiation,  and  the  heat  units  generated  are  computed  by  mul- 
tiplying the  weight  of  water  in  b  by  the  corrected  rise  of  tem- 
perature, and  applying  a  correction  for  the  water  equivalent  of 
the  metal  bomb  and  the  brass  vessel;  that  is,  the  weight  of 
the  metal  parts  multiplied  by  their  average  specific  heat. 


ANALYSIS  OF  COAL  AND  COKE 


PROXIMATE  ANALTSIS 

148.  A  proximate  analysis  of  coal  is  the  one  nearly 
always  required;  and,  although  the  results  obtained  are,  to  a 
great  extent,  merely  comparative,  yet,  when  the  directions 
given  are  strictly  followed,  the  results  obtained  are  accurate 
enough  to  be  of  great  service  in  determining  the  value  of 
the  coal  for  various  purposes.  It  is  of  the  utmost  impor- 
tance that  the  directions  given  should  be  followed  exactly  in 
every  case,  for  slight  variations  in  the  method  give  large 
differences  in  the  results;  and  as  the  results,  so  far  as 
moisture,  volatile,  combustible  matter,  and  fixed  carbon 
are  concerned,  are  only  comparative,  they  must  be  obtained 
under  exactly  the  same  conditions  in  every  case  if  they  are 


92  FUELS  §  16 

to  be  of  any  value.     The  following  is  the  standard  method 
recommended  by  the  American  Chemical  Society. 

149.  Sampling. — In  selecting  a  sample,  about  5  pounds 
of  the  coal  should  be  taken,  exercising  care,  of  course,  to  get 
a  sample  representing  the  whole  quantity.     Break  this  up 
and  quarter   it   down   until  a  sample   weighing  about  100 
grams    is   left.     Pulverize    this,    and   keep   it   in    a    tightly 
stoppered  bottle  until  analyzed.     The  quartering  and  pul- 
verizing should   be    carried    on  as  rapidly  as   possible,   to 
prevent  the  absorption  or  the  loss  of  water,  and,  as  coal  in 
the  powdered   form   changes  in  other   respects,   especially 
when  exposed  to  air,  it  should  be  kept  in  a  tightly  stop- 
pered bottle,  and  the  analysis  should  be  made  as  soon  as 
convenient  after  the  sample  is  taken.     A  method  of  analysis 
recommended  by  the  American  Chemical  Society,  that  gives 
concordant  results,  and  is  probably  more  largely  used  than 
any  other  at  the  present  time,  is  as  follows: 

150.  Moisture. — When  coal  is  dried  at  a  temperature 
slightly  above  212°  F.,  it  loses  in  weight  for  a  time,  and 
then  begins  to  grow  heavier.     Consequently,  dry  all  samples 

for  a  certain  time  at  a  fixed  tempera- 
ture to  obtain  comparative  results. 

The  following  method  of  doing  this 
has  been  generally  adopted:  Weigh 
1  gram  of  the  pulverized  sample  in  a 
porcelain  or  platinum  crucible.  Place 
the  crucible,  uncovered,  in  an  air  bath 
having  a  temperature  from  219°  to 
225°  F.,  and  heat  it  at  this  temperature 
FlG- 14  for  exactly  1  hour.  Place  the  crucible 

in  a  desiccator,  Fig.  14,  cover  it,  allow  it  to  cool.    As  soon  as 
cool,  weigh  covered,  and  call  the  loss  in  weight  moisture. 

151.  Kent's  Method.* — The  following  method  of  deter- 
mining moisture  has  been  proposed  by  Wm.  Kent,  who  claims 
that  it  gives  more  accurate  results  for  western  coals  than 
the  standard  method,  but  it  has  not  been  accepted  by  the 

*Recommended  by  Committee  on  Boiler  Tests  of  the  A.  S.  M.  E. 


§16  FUELS  93 

American  Chemical    Society  and  is  not    generally  used  by 
commercial  chemists. 

Weigh  from  10  to  20  grams  of  the  sample  coarsely  crushed 
in  a  common  coffee  mill  into  a  porcelain  crucible  or  other 
dish.  Place  the  crucible,  uncovered,  in  an  air  bath  having  a 
temperature  ranging  from  240°  to  280°  F.,  and  heat  it  at  this 
temperature  for  1  hour.  Place  the  crucible  in  a  desiccator, 
cover  it,  and  allow  it  to  cool.  As  soon  as  cool,  weigh 
uncovered,  and  call  the  loss  -in  weight  moisture.  Heat 
again  for  i  hour  at  280°  F.,  cool  and  weigh,  and  repeat  the 
operation  until  the  weight  ceases  to  decrease.  The  total 
loss  of  weight  by  drying  is  recorded  as  the  moisture. 

152.  Volatile  Combustible  Matter. — Weigh  1  gram 
of    the    pulverized    sample    into    a    clean  platinum   crucible 
weighing  20  to  30  grams  and  having  a  tightly  fitting  cover. 
Place  the  cover  on  tight  and  heat  over  a  good  Bunsen  burner 
for  exactly  7  minutes.     The  burner  should  be  adjusted  so 
that  it  gives  a  good  flame  20  centimeters  (7.87  inches)  high. 
The  crucible  should  be  supported  on  a  platinum  triangle  so 
that  the  bottom  is  7  centimeters  (2.76  inches)  above  the  top 
of  the  burner.    The  determination  should  be  made  in  a  place 
free  from  drafts.     Cool  the  crucible  in  a  desiccator  and  weigh 
as  soon  as  cool.     From  the  loss  in  weight  caused  by  this 
treatment,    subtract    the    amount    of    moisture    found;    the 
remainder  is  the  volatile  combustible  matter.     This  deter- 
mination should  always  be  made  on  a  fresh  sample  of  coal 
and  not  on  the  sample  used  for  the  determination  of  moisture. 

153.  Fixed    Carbon  and   Ash. — After  weighing    the 
crucible  for  the  determination  of  volatile  combustible  matter, 
draw  the  cover  a  little  to  one  side,  place  the  crucible  in  an 
inclined  position  on  a  triangle,  as  shown  in  Fig.  15,  place  a 
good    Bunsen  burner  under  it,   and  heat  until  the  carbon 
is  completely  burned  off.     This  operation  is  likely  to  prove 
tedious,  and  may  be  hastened  by  letting  the  crucible  cool 
from  time  to  time,  and  by  stirring  the  contents  with  a  stout 
piece  of  platinum  wire,  taking  care,  of  course,  not  to  lose  any 
of  the  material  in  the  crucible  while  stirring  it  up.     Care 


94 


FUELS 


§16 


must  also  be  taken  not  to  produce  too  strong  a  current  of  air 
in  the  crucible  while  heating  it,  as,  in  this  way,  particles  may 
be  carried  out,  and  a  fictitious  value  given  to  the  coal  or  coke 
by  the  apparent  increase  in  fixed  carbon  and  decrease  in  ash. 
When  the  residue  in  the  crucible  no  longer  shows  any  unburned 
carbon,  heat  it  a  few  minutes  longer,  then  cool  it  in  a  desic- 
cator and  weigh.  The  difference  between  this  weight  and 


FIG.  15 

that  at  the  beginning  of  the  operation  is  the  weight  of  fixed 
carbon  in  the  sample,  and  the  substance  remaining  in  the 
crucible  is  ash.  The  percentages  of  the  different  constituents 
are,  of  course,  calculated  in  the  usual  manner.  The  sum  of 
the  percentages  of  fixed  carbon  and  ash  is  approximately  the 
percentage  of  coke  that  may  be  obtained  from  the  coal. 

154.  Sulphur. — Sometimes  the  percentage  of  sulphur 
is  desired  in  connection  with  the  proximate  analysis;  it  is 
obtained  in  a  separate  determination  by  the  method  used  in 
ultimate  analysis.  Thus,  for  coal,  weigh  out  1  gram  of  the 
pulverized  coal  or  coke  and  mix  thoroughly  with  1.5  grams 
of  Eschka  mixture  (see  Art.  156)  in  a  thin  platinum  dish 
of  from  75  to  100  cubic  centimeters  capacity.  A  large 


§  16  FUELS  95 

crucible  may  be  used  instead  of  a  dish.  Support  the  dish 
on  a  triangle  and  heat  slowly,  holding  the  burner  in  the  hand 
at  first.  If  the  gas  ordinarily  used  contains  sulphur — and  all 
coal  gas  does — an  alcohol  lamp  should  be  used  instead  of  a 
Bunsen  burner.  Stir  the  mixture  frequently  with  a  platinum 
wire  and  keep  the  flame  in  motion,  only  touching  the  dish 
with  the  flame  until  strong  glowing  has  ceased.  Then 
gradually  increase  the  heat  until,  in  about  15  minutes,  the 
bottom  of  the  dish  is  at  a  low  red  heat.  Keep  at  this 
temperature,  stirring  every  few  minutes  with  the  platinum 
wire,  until  the  carbon  has  completely  burned;  this  will 
usually  require  about  1  hour.  When  the  carbon  is  com- 
pletely burned,  allow  the  dish  to  cool,  transfer  the  mass  to  a 
beaker,  and  rinse  out  the  dish,  using  about  50  cubic  centi- 
meters of  water.  Add  15  cubic  centimeters  of  a  saturated 
solution  of  bromine  in  water,  boil  for  5  minutes,  allow  to 
settle,  decant  the  clear  liquid  through  a  filter,  add  30  cubic 
centimeters  of  water  to  the  residue  in  the  beaker,  boil 
5  minutes,  allow  to  settle,  decant  the  clear  liquid  through 
the  filter,  and  boil  the  residue  again  for  5  minutes  with 
30  cubic  centimeters  of  water.  Filter  through  the  same 
paper  and  wash  until  a  few  drops  of  the  liquid  running 
through  the  funnel  gives  no  precipitate  when  acidified  with 
nitric  acid  and  tested  with  silver  nitrate.  The  total  volume 
of  the  liquid  in  the  beaker  under  the  filter  should  now  be 
about  200  cubic  centimeters.  Add  2  cubic  centimeters  of 
concentrated  hydrochloric  acid  and  boil  until  the  bromine 
is  completely  expelled.  Test  a  drop  of  the  liquid  with 
litmus  paper  to  make  sure  that  it  has  an  acid  reaction.  If 
not  acid,  add  one  or  two  drops  of  hydrochloric  acid  and 
again  boil.  When  all  the  bromine  has  been  driven  off  and 
the  liquid  is  slightly  acid,  add  slowly  to  the  solution,  which 
should  be  kept  at  about  the  boiling  point,  10  cubic  centi- 
meters of  a  10-per-cent.  solution  of  barium  chloride.  Stir 
constantly  while  adding  the  barium  chloride,  and  add  it 
slowly,  not  more  than  one  drop  a  second. 

Stand  the  beaker  in  a  warm  place  for  the  precipitate  to 
settle;    filter,   wash    thoroughly  with    hot   water   acidulated 


96  FUELS  §  16 

with  a  few  drops  of  hydrochloric  acid,  ignite  moderately,  and 
weigh  as  barium  sulphate,  jBaSOt,  which  contains  13.73  per 
cent,  of  sulphur. 

155.  Although  chemicals  that  are  absolutely  free  from 
sulphur  may  be  obtained  for  this  determination,  a  careful 
blank  should  be  run  with  each  new  lot  of  reagents,  for  some 
so-called  C.  P.  (chemically  pure)  chemicals  are  not  strictly 
as  represented. 

156.  Eschka  Mixture. — Weigh  out  a  convenient  quan- 
tity of  magnesium  oxide,  which  must  be  free  from  sulphur 
and  has  been  previously  ignited  to  expel  all  moisture;   add 
to  this  half  its  weight  of  pure  dry  sodium  carbonate,  grind 
them  together  until    they  are  thoroughly  mixed,  and  keep 
the  mixture  in  a  tightly  stoppered  bottle.     A  bottle  with  a 
ground  glass   stopper  is  preferred  for  this  purpose;    at  all 
events,  the  mixture  must  be  kept  dry. 


ULTIMATE  ANALYSIS 

157.  In  the  ultimate  analysis  of  coal  and  other  fuels, 
a  chemist's  combustion  furnace  is  used.     The  process  is  a 
tedious  and  difficult  one,  and  requires  the  facilities  of  a  good 
laboratory,  and  considerable  experience  in  chemical  manipu- 
lation.    For  details  of  the  method,  treatises  on  analytical 
chemistry  should  be  consulted. 

158.  Notes. — The  following  is  a  convenient  method  of 
keeping  the  notes  of  a  coal  analysis: 

Weight  of  crucible  and  coal 32.000  grams 

Weight  of  crucible 30.000  grams 

Coal  taken 2.000  grams 

Weight  of  crucible  +  coal 32.000 

Weight  of  crucible  +  coal,  after  drying     .    .    .31.992 

Loss  =  water 008  =      .40  per  cent. 

Weight  of  crucible  +  coal,  dried 31.992 

Weight  of  crucible  +  coal,  heated  (closed)  .    .  31.448 

Loss  =  volatile  combustible 544  =  27.20  per  cent. 


§  16  FUELS  97 

Weight  of  crucible  +  coal,  heated  (closed)  .  .  31.448 
Weight  of  crucible  +  coal,  heated  (open)  .  .  30.100 
Loss  =  fixed  carbon 1.348  =  67.40  per  cent. 

Weight  of  crucible  +  contents,  heated  (open)   30.100 

Weight  of  crucible 30.000 

Residue  =  ash 100  =    5.00  per  cent. 

Sulphur 1.00  per  cent. 

REPORT 

Moisture .40  per  cent. 

Volatile  combustible 27.20  per  cent. 

Fixed  carbon 67.40  per  cent. 

Ash     .   . .  5.00  per  cent. 

100.00  per  cent. 

NOTE.— The  several  percentages  are  found  by  dividing  each  remainder  by  the 
weight  of  the  original  sample,  which  in  this  case  was  2  grams. 

For  accurate  analysis  a  good  balance  is  essential,  but  for  the 
work  outlined  above,  a  druggist's  scales  will  give  fair  results. 


REPORT  OF  ANAL.Y8I8 

159.  The  proximate  analysis  of  a  coal  may  be  reported 
in  three  forms,  as  percentages  of  the  moist  coal,  of  the  dry 
coal,  and  of  the  combustible,  as  explained  in  Art.  10. 


COAL  HOISTING,  CONVEYING,  AND 
STORING 

160.  Until  within  recent  years,  the  only  method  of  han- 
dling coal  after  it  had  reached  its  destination  in  the  cars  or 
boats  in  which  it  was  shipped,  was  the  use  of  the  shovel  and 
wheelbarrow.  The  first  improvement  on  this  method  was 
the  use  of  elevated  trestles  with  inclined  planes  and  pockets 
or  bins  under  the  trestles.  Cars  were  run  on  to  the  trestles 
and  the  coal  was  dumped  into  the  bins  through  movable 
doors  provided  in  the  bottoms  of  the  cars.  If  the  bottoms 
of  the  coal  pockets  were  raised  high  enough  chutes  were 
provided,  through  which  the  coal  could  be  run  into  carts. 
For  unloading  boats,  a  simple  rope  hoist  and  a  bucket  were 
commonly  used,  the  hoist  being  operated  by  a  horse  or 


98  FUELS  §16 

small  steam  engine  and  the  bucket  filled  by  men  with 
shovels. 

The  vast  growth  of  the  coal  trade,  and  the  fluctuations  of 
supply  and  demand,  which  make  it  desirable  to  store  mil- 
lions of  tons  of  coal  near  the  points  of  largest  consumption 
during  certain  seasons,  have  led  to  the  development  of 
systems  of  hoisting  and  conveying  machinery,  by  means  of 
which  coal  can  be  unloaded  and  stored  or  reloaded  into  cars 
at  an  expense  of  only  3  or  4  cents  per  ton.  The  erection  of 
power  houses  in  cities  on  valuable  real  estate  has  also 
necessitated  the  erection  of  large  storage  coal  bins  above  the 
boiler  houses  from  which  coal  may  be  delivered  to  the  boilers, 

The  principal  means  of  cheaply  handling  and  transferring 
coal  in  large  quantities  from  one  point  to  another,  are  the 
following:  (1)  Self-filling  buckets;  (2)  flight  conveyers; 
(3)  belts;  (4)  continuous  trains  of  iron  buckets;  (5)  chutes; 
(6)  car-dumping  machines. 


SELF-FUSING  BUCKETS 

161.  Self-filling   buckets    are    made   in    the    several 
forms  shown  in  Figs.  16  to  19  and  are  largely  used  where  the 
coal  can  be  attacked  from  above.     They  are  hoisted  by  ropes 
wound  on  drums  operated  by  steam  engines  or  electric  motors 
and  are  transferred  from  place  to  place  by  derricks  or  cranes 
of  various  types.     Many  of  them  dump  automatically. 

162.  The  clam-shell  bucket,  Fig.  16  (a)  and  (6),  con- 
sists of  two  shells  a  that  are  supported  by  rods  b  from  the 
yoke  c  and  connected  at  d  by  a  journal  <?.     On  the  journal  is 
the  pulley  /  to   which  the  chain  g  is  attached  to  a  pin  h. 
When  the  chain^  is  taut,  the  bucket  is  closed,  as  in  (a), 
and  the  slack  of  the  chains  i  i  is  coiled  about  the  journal  e. 
When  the  chain  g  is  loosened,  the  weight  of  the  bucket  and 
the  pulley  h  assisted  by  any  material  in  the  bucket  causes 
the  bucket  to  open,  as  in  (b}.     When  the  chain  g  is  pulled 
upwards,  the  bucket  closes  and  fills  with  the  material  to  be 
hoisted.      The  entire  bucket  and  attachment  is   raised   and 
lowered  by  means  of  the  rope  /  working  about  the  pulley  k. 


§16 


FUELS 


99 


163.     The  orange-peel   self-filling  type  of    bucket, 
Fig.  17  (a)  and  (b}>  works  very  similarly  to  the  clam  shell. 


When  the  chain  g  that  is  coiled  about  the  pulley  h  is  pulled 
up,  it  raises  this  pulley  and  thus  raises  the  end  k  of  an  arm 


PIG.  17 


that  is  attached  to  the  side  a  of  the  bucket  and  this  closes 
the  bucket. 


100 


FUELS 


§16 


Clam-shell    and    orange-peel    buckets    are    made    with    a 
capacity  varying  from  15  cubic  feet  to  5  cubic  yards  and 


FIG.  18 

varying  in  weight  from  2,200  to  18,000  pounds.  With  such 
buckets  60  to  80  per  cent,  of  a  ship's  cargo  can  be  unloaded 
without  hand  shoveling. 

164.  The   drop-bottom   bucket, 

Fig.  18,  is  loaded  as  shown  and  un- 
loaded by  loosening  the  catch  a  so  that 
the  bottom  b,  which  is  hinged  at  c, 
drops  downwards. 

165.  The  shovel  bucket,  shown 
in  Fig.  19,  is  loaded  similarly  to   the 
one  shown  in  Fig.   18,  but  is  dumped 
automatically    by    turning    over   when 
the  catch  a  is  loosened. 


CRANES 
166.     The  Locomotive  Crane. 

FlG-  19  Fig.   20   shows   a    locomotive   crane 

used  for  unloading  coal  by  means  of  a  clam-shell  or  orange- 
peei  bucket  and  transferring  it  from  a  boat  to  a  railroad  car 
or  from  a  car  to  a  boat.  The  crane  runs  on  tracks  a  a  placed 


FUELS 


101 


between  the  boat  and  the  car.     The   gauge  of  the  tracks 
depends  on   the  radius  of  the   crane  swing  and  when  not 
already  fixed  by  existing  tracks  is  about  as  follows: 
4  feet  83  inches  for  a  maximum  radius  of  swing  of  30  feet 
14  feet  6  inches  for  a  maximum  radius  of  swing  of  45  feet 
16  feet  for  a  maximum  radius  of  swing  of  60  feet 
20  feet  for  a  maximum  radius  of  swing  of  100  feet 


PIG.  20 

Steam  or  electric  power  may  be  used  to  propel  the  crane 
along  its  tracks  and  to  operate  the  bucket.  The  operator, 
who  is  on  the  covered  platform,  closes  and  thus  loads  the 
bucket,  hoists  and  dumps  it,  and  at  the  same  time  that  he 
is  hoisting  it  revolves  the  crane.  A  speed  of  one  bucket 
per  minute  for  all  sizes  and  loads  is  a  fair  average,  though 
this  speed  is  often  exceeded. 


102 


§16 


FUELS 


103 


167.  Overhead    Crane. — The    overhead    crane    for 

unloading  coal,  Fig.  21,  runs  on  tracks.  The  bucket  a, 
which  is  loaded,  hoisted,  and  transported  along  the  track  bb 
by  machinery  located  in  the  shed  c,  is  dumped  either  into  a 
box  car,  a  gondola,  or  on  a  stock  pile  as  desired. 

168.  The  fixed  steel  derrick,  Fig.  22,  is  used  for  hoist- 
ing coal  buckets  and  dumping  them  into  a  car  or  bin  at  a 
higher  level.     In  the  illustration,  the  coal  is  dumped  from 
the  cars  into  the  hopper  a,  which  discharges  into  the  bucket 


PIG.  22 

through  a  short  chute,  as  shown.  The  bucket  dumps  auto- 
matically into  the  hopper  d,  which  discharges  into  the  car  c, 
which  is  carried  away  and  dumped  by  means  of  the  Hunt 
automatic  railway,  shown  in  Fig.  23.  The  car  c  runs  down 
the  inclined  plane  d  and  at  a  given  point  it  comes  in  contact 
with  a  truck  e,  Fig.  23,  which,  by  means  of  the  momentum 
attained  in  going  down  the  plane,  it  pushes  along  the  truck 
and  thus  raises  the  weight  /,  Fig.  22,  until  the  tripping 
mechanism  g  on  the  side  of  the  car  comes  in  contact  with 
the  wedge-shaped  tripping  block  h  alongside  the  track.  The 
two  side  bars  are  connected  by  a  wire  rope  and  the  toggle 

145—29 


104 


FUELS 


§16 


is  so  arranged  that  the  tripping  mechanism  is  on  one  side 
only,  the  weight  of  the  coal  opening  both  doors.  Both  side 
doors  of  the  car  are  opened  at  the  same  time  and  as  the  bot- 
tom of  the  car  has  a  center  ridge  sloping  to  the  sides,  the 


load  dumps  very  quickly  and  evenly  so  that  the  car  will  not 
tip  to  the  side.  When  the  car  has  dumped,  the  weight  /, 
Fig.  22,  falls  and,  by  means  of  the  cross-bar  <?,  pulls  the  car 
along  the  trestling  and  gives  it  sufficient  momentum  to 
return  up  the  inclined  plane  to  the  chute. 


CONVEYERS 


FLIGHT    CONVEYERS 

169.  Flight  conveyers,  which  are  used  to  convey 
coal  horizontally  or  up  an  incline,  consist  of  a  trough,  made 
of  timber  and  lined  with  iron,  or  entirely  of  iron  or  steel, 
and  a  chain  or  wire  rope,  to  which  iron  plates,  or  flights, 
are  attached  at  frequent  intervals  at  right  angles  to  the 


1C 


FUELS 


105 


chain  or  rope.     These  drag  the  coal  along  the  trough,  the 
chain  or  rope  being  driven  by  suitable  gearing.     There  is  a 


FIG.  24 

large  variety  of  these  flights,  differing  in  structural  details, 
but   all    acting    on    the 
same  principle. 

Fig.  24  shows  a  sim- 
ple form  of  single- 
strand  flight  conveyer 
for  light  work  with  over- 
head return.  Similar 
conveyers  with  double 
strands  for  carrying  the 
flight  are  much  used  for 
conveying  anthracite 
from  the  mine  to  the  top 
of  the  breaker. 

Fig.  25  shows  a  sim- 
ilar form  for  heavy  work 
where  a  double  chain  is 
used,  carried  on  rollers 
to  avoid  the  noise  produced  by  a  conveyer  in  which  the  flight 
drags  on  the  bottom. 


FIG.  25 


106 


FUELS 


§16 


Fig.  26   shows    a   form    much   used   for   conveying   coal 
that  is  in  large  lumps. 


Fig.  27  shows  a  conveyer  in 
which  disks  of  metal  are  attached 
to  a  wire  cable  or  to  a  chain. 


BELT    CONVEYERS 

170.  Belts,  made  of  layers  of 
canvas  and  rubber  and  moving  at 
high  speeds,  are  rapidly  coming 
into  use  as  coal  conveyers,  and  by 
them  a  constant  stream  of  coal 
may  be  carried  horizontally  or  up 
inclinations  as  great  as  26°. 

Fig.  28  shows  the  cross-section 
of  half  the  width  of  a  conveying 
belt  composed  of  a  canvas  core 
covered  with  specially  prepared 
tough  rubber  that  is  thickest  in  the 
center,  where  the  most  wear  comes. 
FIG.  27  The  loaded  belt,  Fig.  29,  is 

supported  on  rollers  or  idlers  placed  so  as  to   shape  the 
belt    into    the    form    of    a    trough.     The    empty   returning 


belt    is    supported    on    horizontal    rollers   b.     The    upper 
idlers  are  placed  6  feet  or  less  apart  depending  on  the  load  on 


§16 


FUELS 


107 


the  belt  and  the  width  of  belt,  the  wider  the  bait  and  the  heavier 
the  load,  the  closer  are  the  idlers.  The  bottom  idlers  for  the 
returning  belt  are  placed  8  to  12  feet  apart. 


FIG.  29 

171.     A  tripper,  Fig.  30,  is  used  where  it  is  desired  to 
discharge   the    material   carried   by  the    belt   at   any  point 


excepting  at  the  head  end.     This  tripper  consists  of  two 
pulleys  a,  a'  placed  so  that  the  belt  runs  over  one  and  under 


108 


FUELS 


§16 


§  1C  FUELS  109 

the  other.  When  the  belt  makes  the  first  bend,  it  discharges 
its  load  into  a  chute  as  shown.  The  tripper  may  be  fixed  so 
as  to  discharge  at  a  distinct  point  along  the  belt,  or  it  may  be 
moving  so  as  to  discharge  uniformly  along  the  whole  or  any 
part  of  the  length  of  the  belt. 

172.  An  installation  of  the  Robins  belt  conveyer  located 
at  the  coke  works  of  Jones  &  Laughlin,  Pittsburg,  Penn- 
sylvania, and  having  a  capacity  of  500  tons  per  hour,  is 
shown  in  Fig.  31.  A  large  elevator,  consisting  of  a  double 
row  of  steel  buckets,  elevates  the  coal  to  the  belt  conveyer, 
which  carries  it  across  the  tracks  of  a  railroad  and  distributes 
it  by  means  of  an  automatic  tripper  into  hoppers. 


BUCKET    CARRIERS 

173.  Bucket  carriers  consist  of  series  of  buckets 
attached  to  an  endless  chain  or  link  belt,  which  passes  over 
and  receives  its  motion  from  suitable  pulleys  or  sprocket 
wheels,  which  are  connected  by  gearing  or  belting  to  some 
source  of  power.  The  buckets  frequently  join  or  overlap  so 
that  a  practically  continuous  stream  of  material  is  carried. 


174.  The  simplest  form  of  bucket  carriers,  Fig.  32,  con- 
sists of  a  series  of  buckets  rigidly  attached  to  a  link  belt, 
which  passes  over  sprocket  wheels  at  its  two  ends.  To 
prevent  sagging,  the  ends  of  each  link  are  fitted  to  axles 
having  a  wheel  at  each  end;  these  wheels  roll  on  tracks 
placed  on  each  side  of  the  conveyer  line.  The  load  is 


110 


FUELS 


§16 


received  at  any  point  along  the  line  and  is  discharged  over 

the  end. 

Fig.  33  shows  a  bucket  elevator  having  buckets  rigidly 

attached  to  a  chain  that  passes  over  sprocket  wheels  at  the 

top  and  bottom,  the  bottom  sprocket  being  placed  in  a  boot 

where  the  buckets  receive  their  loads. 

Instead  of  being  rigidly  connected  to  the  chain,  the  buckets 

are  frequently  so  balanced  and  hung  from  the   supporting 

belt  or  chain  that  they  remain  upright  whether  the  chain 

is  horizontal,  vertical,  or  in- 
clined. Such  carriers  are 
also  usually  arranged  so  that 
they  can  be  loaded  or  dis- 
charged automatically  at  one 
or  a  number  of  points. 
Great  ingenuity  has  been 
displayed  by  manufacturers 
in  adapting  the  buckets  and 
the  arrangements  for  oper- 
ating them  to  the  varied 
conditions  under  which  such 
carriers  must  be  used,  and 
it  is  possible  therefore  to 
give  only  a  few  of  the  com- 
moner uses. 

175.  Fig.  34  shows  a 
train  of  link-belt  overlap- 
ping carrier  buckets.  The 

bucket  a  is  pivoted  at  b  between  two  link  belts  c,  which 
are  supported  by  wheels  d  running  on  a  track  <?,  which 
may  be  horizontal,  inclined,  or  vertical.  The  coal  is  loaded 
from  the  automatic  hopper  /  into  the  buckets.  The  line  of 
buckets  is  driven  by  the  sprocket  wheel  h  which  is  driven  by 
the  gearing  shown;  power  to  operate  the  automatic  feeder  / 
is  taken  from  the  sprocket  wheel  g  by  gearing.  The  buckets 
are  dumped  at  any  desired  point  by  fixed  dumping  blocks  or 
by  the  movable  automatic  dumper  z. 


112  FUELS  §16 

176.  Fig.  35  shows  another  form  of  bucket  for  trans- 
ferring material  horizontally  and  another  dumping  device. 
The  buckets  are  secured  on  one  side  only  to  a  single  chain  a, 
and  when  the  wheels  b  enter  the  guide  track  c  the  bucket 
turns  upside  down  and  discharges  into  the  chute  d.  The 
dumping  frame  e  runs  on  the  wheels  /  and  by  shifting  will 
distribute  the  coal  at  any  point  desired. 


FIG.  35 

177.  Fig.  36  shows  the  application  of  such  a  transfer 
system  a  used  in  connection  'with  some  form  of  bucket  or 
belt  elevator  b,  which  takes  the  coal  from  a  hoppers  beneath 
a  car  and  elevates  it  into  the  bin,  where  the  transfer  system 
distributes  it  uniformly  around  the  bin.     A  square  storage 
bin  is  considered  cheaper  than  a  long,  narrow  one,  and  a  dis- 
tributing system,  such  as  is  shown  in  Fig.  36,  permits  such 
a  bin  to  be  filled  uniformly  instead  of  only  partially,  as  is  the 
case  when  the  material  is  all  dumped  along  the  center  line, 
as  shown  by  the  dotted  lines. 

178.  Fig.   37  shows  an  arrangement    of  a  locomotive 
coal   and   ashes    handling    station  of  the  Philadelphia  and 


§16 


FUELS 


113 


Reading  Railroad.  The  coal  drops  from  the  cars  in  which 
it  is  received  into  a  pocket  a,  from  which  it  is  fed  into  the 
elevating  buckets  b,  which  deliver  it  to  a  chute  c,  from 
which  a  horizontal  flight  conveyer  distributes  it  to  any  point 


FIG. 86 


along  the  length  of  the  storage  pile.  Another  bucket  con- 
veyer d  receives  the  ashes  from  the  locomotives  and  elevates 
them  to  a  storage  bin  <?,  whence  a  chute  delivers  them  to  the 
cars  /,  in  which  they  are  removed.  A  similar  arrangement 
can  be  used  for  supplying  coal  to  a  boiler  house. 


114 


FUELS 


§16  FUELS  115 


CHUTES 

179.  Chutes  are  often  used  for  conveying  coal  from  a 
bin,  pocket,  or  car  into  a  vessel,  pocket,  or  pile.     Such  chutes 
must  be  arranged  so  as  to  subject  the  coal  to  a  minimum  of 
shock,  so  as  to  avoid  breakage.     To  accomplish  this,  they 
are  usually  made  adjustable  so  that  they  can  be  raised  and 
lowered  at  will,  and  the  lower  end  of  the  chute  kept  close 
to  the  top  of  the  pile  of  coal.     By  doing  this  and  by  keeping 
the  chute   full,   the   coal   slides  slowly  and  does  not  drop, 
thus  avoiding  breakage. 

180.  Fig.  38  shows  a  common  method  of  loading  vessels 
by  means  of  an  adjustable  chute.     The  coal  is  dumped  from 
the  car  into  the  pocket  a,  which  may  be  of  any  desired  size, 
and  if  space  permits  may  be  used  for  storage  purposes. 
These  pockets  usually  contain  only  a  small  amount  and  they 
serve  merely  as  a  hopper  to  feed  the  chute.     A  vertically 
sliding  hopper  b  permits  adjustment  for  height  of  tide  and 
the  depth  of  the  vessel.     The  delivery  of  the  coal  is  con- 
trolled by  a  regulating  gate  c ,  and  the  flow  is  shut  off  by  the 
gate  d. 

With  anthracite,  screens  to  take  out  the  fine  coal  are  placed 
at  some  point  in  the  chute,  often  at  the  bottom  e  of  the  sliding 
chute  b.  Instead  of  an  open  chute  as  shown,  telescopic  pipe 
chutes  are  sometimes  used,  that  is,  one  part  slides  within 
another,  so  that  the  end  may  be  kept  close  to  the  pile  of  coal. 

181.  Pitch  of  Chutes. — The  following  may  be  taken 
as  average  figures  for  the  angle  or  grade  of  chutes  for  anthra- 
cite to  be  used  where  the  chutes  are  lined  with  sheet  steel: 
For  broken  or  egg  coal,  2i  inches  per  foot;    for  stove  or 
chestnut  coal,  3i  inches  per  foot;  for  pea  coal,  4i  inches  per 
foot;   for  buckwheat  coal,  6  inches  per  foot;    for  rice  coal, 
7  inches  per  foot;  for  culm,  8  inches  per  foot. 

If  the  coal  is  to  start  on  the  chute  by  gravity,  1  inch  per 
foot  should  be  added  to  each  of  the  above  figures;  while  if 
the  chutes  are  lined  with  manganese  bronze  in  place  of  steel, 
the  above  figures  can  be  reduced  1  inch  per  foot  for  coal 


116 


FUELS 


§16 


in  motion,  or  would  remain  as  given  to  start  the  coal. 
When  the  run  of  mine  is  to  be  handled,  the  angle  should  be 
not  less  than  5  inches  per  foot,  or  practically  22i°  from  the 


FIG.  38 

horizontal.  If  chutes  are  lined  with  glass,  the  angle  can  be 
reduced  from  30  per  cent,  to  50  per  cent.,  depending  some- 
what on  the  nature  of  the  coal.  In  all  cases,  the  flatter  the 
coal,  the  steeper  the  angle  must  be,  on  account  of  the  large 


§16 


FUELS 


117 


friction  surfaces  exposed,  com- 
pared with  the  weight  of  the 
piece.  If  chutes  are  lined  with 
cast  iron,  the  angle  should  be 
about  the  same  as  that  em- 
ployed for  steel,  though  some- 
times a  slightly  greater  angle 
is  allowed. 

When  run-of-mine  bitum- 
inous coal  is  •  to  be  handled, 
the  angle  of  the  chutes,  if  iron 
or  steel  lined,  should  be  about 
32°  from  the  horizontal,  but  if 
not  lined,  an  angle  of  45°  may 
be  required.  If  the  coal  is 
wet,  the  angle  should  always 
be  steeper  than  when  it  is  dry, 
and  coarse  coal  will  slide  on  a 

3    flatter  angle  than  slack  or  fine 

I    coal.  

COMBINATIONS  OF  HOIST- 
ING AND  CONVEYING 

SYSTEMS 

182.  Fig.  39  shows  dia- 
grammatically  how  several  of 
the  forms  of  conveying  and 
hoisting  apparatus  already  ex- 
plained may  be  combined  in 
one  plant.  The  coal  may  be 
taken  from  the  scow  a,  by  any 
form  of  bucket  and  the  bucket 
transferred  above  the  bin  b  by 
^  any  form  of  derrick.  Then 
|  from  b,  it  passes  through  by  a 
|  chute  and  is  carried  up  the 
]  incline  by  a  flight  conveyer  c, 
|  by  a  bucket  train,  or  by  a  belt, 


118  FUELS  §16 

and  at  the  head  it  empties  into  the  bin  d  and  is  distributed  by 
a  conveyer,  such  as  is  shown  in  Fig.  36.  The  coal  bin  may 
also  be  filled  from  the  cars  by  dumping  the  coal  into  the  hop- 
per e,  and  then  elevating  it  by  a  bucket  elevator  as  shown. 
The  apparatus  on  either  end  can  also  be  arranged  to  operate 
in  the  reverse  direction  from  that  described,  so  that  d  can  be 
used  as  a  storage  bin  and  be  unloaded  into  either  the  barge 
or  the  car. 

CAR-DUMPING  MACHINE 

183.  During  the  past  few  years,  several  styles  of  car- 
dumping  machines  have  been  introduced,  in  which  a  railroad 
car  filled  with  coal  is  lifted  bodily  and  either  tipped  up  end- 
wise so  that  the  coal  slides  out  from  a  hinged  door  at  the 
end,  or  rotated  parallel  to  its  length  so  as  to  pour  the  coal 
out  from  one  side. 

184.  The  Brown   car-dumping  machine    is    shown 
in  Fig.  40;  the   car  a   is  pushed    by   the   barney  b  on  to   a 
cradle  c,   where   it  is   clamped   on  the   top  and  sides    with 
hydraulic  clamps,  and  the  cradle  is  then  slowly  raised  and 
turned   over  until  the  car  is    upside  down,  thus    gradually 
discharging  its  contents  through  six  hopper  compartments  d 
attached    to    the    cradle    into    a    series    of   transfer  tubs  e, 
which  are  resting  on  a  flat  car  on  an  adjoining  track.     This 
transfer  flat  car  is  then  run  to  any  point  desired,  and  the 
tubs  lifted  by  a  crane  /  to  the  position  g  and  run  out  to  h 
and  dumped  on  a  stock  pile  or  into  the  hold  of  a  vessel. 
As  the  full  transfer  tubs  are  being  moved  out  of  the  way  and 
empty  ones    put  in  place,   the   cradle  is  lowered   and   the 
empty  car  replaced  by  a  full  one.     The  system  has  been  so 
thoroughly  perfected  that  in  loading  a  vessel  from  cars  the 
coal  is  handled  without  breakage.      The  vessel  is  kept  on 
even  keel  while  loading;  the  entire  cargo  is  put  aboard  with- 
out moving  the   vessel;   the  vessel  is  loaded   rapidly    and 
economically,  and  the  loaded  and  empty  cars  are  moved  to 
and  from  the  machine  by  a  car-pushing  device  without  the 
aid  of  a  locomotive. 


FUELS 


119 


120 


FUELS 


§16 


185.  The  McMyler  car-dumping  machine,  Fig.  41, 
consists  of  a  steel  tower,  underneath  which,  and  at  the  track 
level,  is  a  cradle  on  which  the  loaded  car  is  run  to  be  dumped. 


FIG.  41 


The  cars  are  pushed  on  to  the  cradle  from  one  end  and  the' 
empties  off  at  the  other.  The  car  a  is  held  by  clamps  that 
grip  it  when  the  cradle  is  raised  and  hold  it  in  place.  These 
clamps  are  not  shown  in  the  figure  on  account  of  the  tilted 


§  16  FUELS  121 

position  of  the  car.  The  hollow  bars  b  through  which  the 
chains  c  pass  also  support  the  car  when  tilted,  as  shown,  and 
prevent  its  tipping  too  far,  the  weight  of  the  car  being  counter- 
balanced by  the  weights  d  attached  to  the  ends  of  the  ropes  e 
that  slide  up  and  down  the  inclined  legs  of  the  tower.  The 
cradle  and  loaded  car  are  hoisted  by  means  of  ropes  driven 
by  an  engine  placed  between  the  back  legs  of  the  tower.  At 
the  proper  height,  guides  on  the  front  of  the  cradle  strike 
agaipst  stops  on  the  frame  and  hold  the  front  of  the  cradle 
while  the  back  side  continues  to  rise,  thus  turning  both  cradle 
and  car  over  to  the  dumping  position  as  shown.  The  con- 
tents of  the  car  fall  on  the  hopper  /  and  are  delivered  into 
the  hold  of  barge  g  through  the  telescopic  chute  h.  The 
hopper  /  can  be  raised  or  lowered  as  circumstances  may 
require.  As  soon  as  the  car  is  empty  the  cradle  returns  to  a 
horizontal  position  and  is  lowered  to  the  track  level.  The 
empty  car  is  then  pushed  out  of  the  way  by  the  loaded  one 
that  takes  its  place  on  the  cradle.  The  movement  of  the 
cars  is  governed  from  the  house  i  and  the  dumping  from  the 
house  j.  

COAL   STORAGE 

186.  Coal  is  stored:  (1)  to  insure  a  constant  supply  at 
points  where  it  is  to  be  used  and  which  will  not  depend  on 
uncertain  transportation  facilities,  labor  troubles,  etc.;  (2)  to 
permit  of  the  mines  being  run  steadily  even  though  the 
market  for  the  coal  varies  with  the  season,  as  is  the  case 
with  coal  used  largely  for  domestic  purposes,  such  as  anthra- 
cite; (3)  to  take  advantage  of  cheaper  transportation  by 
water,  which  is  open  only  during  a  portion  of  the  year,  as,  for 
instance,  the  Lake  trade  in  the  United  States. 

Bituminous  coal  is  much  less  frequently  stored  in  large 
quantities  than  anthracite,  since  much  of  it  deteriorates  on 
exposure  to  the  weather  and  because  it  is  so  widely  distributed 
throughout  the  country  and  the  demand  for  it  throughout  the 
year  is  quite  uniform. 

A  coal-storage  plant  should  be  arranged  so  that  both  in 
unloading  and  loading  the  coal  it  will  move  by  gravity  as 


122 


FUELS 


§16 


much  as  possible  and  with  the  use  of  the  smallest  possible 
amount  of  machinery,  and  so  that  there  may  be  the  least 
possible  breakage  of  the  coal. 

Pockets  or  bins  are  used  only  for  storing  small  quantities, 
as,  for  instance,  on  ship  piers,  where  there  is  not  room  for  an 
extensive  storage  system. 

Coal  is  usually  stored  in  piles,  which  are  generally 
uncovered.  For  storage  in  large  quantities,  special  facilities 
are  required  and  the  following  are  some  of  the  principal 
methods  now  used. 


FIG. 42 

187.  Side-Hill  Storage.— Where  a  suitable  hillside  is 
available,  the  system  illustrated  in  Fig.  42  may  be  used. 
The  dumping  track  a  is  laid  on  a  trestle  placed  on  top  of  the 
hill  and  the  reloading  track  b  on  a  level  space  at  the  bottom 
of  the  hill  with  an  inclined  plank  floor  between.  The  coal  is 
held  by  a  timber  bulkhead  provided  with  gates  at  frequent 
intervals  for  loading  the  cars  and  supported  on  a  retaining 
wall  c.  To  relieve  the  pressure  on  the  retaining  wall  and  to 
increase  the  stockage  capacity,  a  horizontal  area  is  often  left 
between  the  bottom  of  the  hill  and  the  loading  track,  but 


§16 


FUELS 


123 


much  of  the  coal  on  this  level  space  will   not  run  from  the 
chutes  and  hence  must  be  shoveled. 

188.  Trestle  Storage. — In  this  system,  the  coal  is 
dumped  into  a  pile  from  cars  running  on  the  trestle,  as 
shown  in  Figs.  43  and  44,  and  is  reloaded,  when  needed, 


PlO.  43 

through  chutes  into  other  cars  running  in  a  tunnel  built 
within  the  pile,  as  in  Fig.  43,  or  better  below  it,  as  in  Fig.  44. 
The  grade  of  the  tracks  on  the  trestle  and  in  the  tunnel  may 
be  made  such  that  the  cars  can  be  handled  by  gravity,  by  a 
locomotive,  or  by  a  hoisting  engine,  as  circumstances 


FIG.  44 

require.  The  capacity  of  such  a  plant  may  be  increased  by 
building  retaining  walls  along  the  sides,  but  even  with  such 
retaining  walls,  and  with  the  tunnel  below  the  bottom  of  the 
pile,  a  considerable  amount  of  the  coal  cannot  be  loaded 


124 


FUELS 


§16 


into  the  car  by  gravity,  but 
must  be  shoveled,  thus  con- 
siderably increasing  the  cost 
of  handling. 

Instead  of  stocking  and 
unloading  the  piles  with  cars, 
conveyers  may  be  placed  on 
the  trestle  and  in  the  tunnel, 
and  the  system  thus  made 
more  or  less  automatic. 

189.  The  bridge  tram- 
way storage  system  con- 
sists of  a  steel  bridge 
spanning  the  storage  space, 
and  having  at  one  end  a 
boom  that  extends  out  over 
the  hatch  of  a  vessel  and  is 
sometimes  also  provided  at 
the  other  end  with  a  canti- 
lever extension,  as  shown  at 
c,  Fig.  45. 

A  bucket  traverses  the  sys- 
tem from  the  end  of  the  boom 
to  the  end  of  the  cantilever 
extension  and  may  dump  its 
load  either  into  the  storage 
piles  as  shown,  or  into  cars. 
The  bridge  span  a  is  usually 
from  180  to  190  feet  with  a 
boom  b  30  to  40  feet  long 
and  an  extension  c  of  80  to 
105  feet.  The  ends  of  the 
bridge  are  supported  on  sin- 
gle or  double  A-shaped  frames 
that  are  mounted  on  wheels 
and  run  on  tracks.  The  sys- 
tem is  a  very  flexible  one,  as 


PIG.  46 


126  FUELS  §  16 

the  two  frames  may  be  moved  independently  of  each  other, 
and  the  front  frame  regulated  to  suit  the  unloading  from  the 
hatch  of  the  vessel,  and  the  back  one  to  suit  the  conditions 
at  the  stock  pile.  The  trolley  carrying  the  bucket  is  operated 
from  an  engine  room  placed  either  on  the  front  or  back 
frame  and  either  near  the  ground  or  elevated  so  that  the 
engineer  may  have  a  full  view  of  the  plant.  The  coal  is 
unloaded  from  the  storage  pile  into  the  cars  shown  by  means 
of  the  bucket  used  in  stocking  it,  or  tunnels  may  be  used,  as 
shown  in  Fig.  44. 

190.  The  Dodge  system  of  coal  storage  is  designed 
to  stock  the  coal  in  conical  piles,  outdoors.  The  system  is 
arranged  in  units  of  two  piles  each,  as  shown  in  Fig.  46. 
The  coal  is  stacked  by  means  of  trimming  machines,  of 
which  each  unit  has  two,  one  for  each  pile.  This  trimming 
machine  consists  of  a  truss  arranged  as  shown  and  carrying 
a  flight  conveyer  a  on  one  leg.  This  conveyer  is  fed  with 
coal  from  a  bin  b,  into  which  it  is  dumped  from  cars,  or 
unloaded  from  boats  by  any  of  the  methods  already  described. 

The  trimmer  builds  the  coal  into  conical  piles,  beginning 
the  delivery  just  above  the  ground  line,  and  gradually 
advancing  the  delivery  point,  keeping  it  slightly  above  the 
apex  of  the  growing  pile,  so  that  after  the  coal  drops  from 
the  car  or  bucket  into  the  track  hopper  there  is  no  further 
drop  exceeding  a  few  inches.  The  truss  of  the  trimmer 
spans  the  space  on  which  the  pile  is  to  be  formed  and  the 
legs  are  inclined  at  about  the  natural  angle  of  repose  of  coal. 

The  reloading  is  accomplished  by  a  horizontal  conveyer  c , 
shown  enlarged  in  Fig.  47,  which  is  open  at  one  side  and 
which  is  run  on  circular  tracks  and  is  pivoted  at  one  end  so 
that  it  is  kept  along  the  edge  of  the  coal  pile.  The  con- 
veyer a  delivers  the  coal  to  an  inclined  conveyer  6,  Fig.  47, 
which  carries  it  to  a  reloading  tower,  from  which  it  falls  into 
cars  either  with  or  without  first  being  screened  as  may 
*be  desired. 

For  large  capacities,  the  dumping  tracks  are  arranged  on 
one  side  of  the  plant  and  the  reloading  tracks  at  the  other, 


§16 


FUELS 


127 


so  that  trimming  and  reloading  can  be  carried  on  at  the 
same  time  without  interference  of  the  cars.  Each  unit  is 
designed  to  stock  100,000  tons  of  coal,  that  is,  each  pile 


PIG.  47 


contains  50,000  tons  and  the  capacity  of  each  unit  is  8,000  to 
9,000  tons  per  day  of  10  hours  either  loaded  or  unloaded 
or  both  when  arranged  so  that  both  operations  can  be  carried 
on  simultaneously. 


128 


FUELS 


§16 


This  system  is  particularly  applicable  to  anthracite,  as  it 
permits  the  stocking  of  the  different  sizes  in  different  piles. 

191.     A  system  for  storing  bituminous  coal  is  shown  in 
Fig.  48.     A  locomotive  crane  a  provided  with  a  long  boom  b 


runs  on  a  circular  track  c  around  a  central  hopper  d  into 
which  coal  is  dumped  from  the  cars.  From  this  hopper,  it  is 
lifted  by  a  clam-shell  bucket  and  delivered  to  the  pile.  In 
reloading,  the  crane  takes  coal  from  the  pile  and  delivers 
it  directly  into  cars  or  carts.  This  system  has  a  capacity 


§16 


FUELS 


129 


of  from  40  to  90  tons  per  hour.     The  capacity  of  such  piles 
of  different  sizes  is  given  in  Table  XXX. 

TABLE  XXX 
DODGE    BITUMINOUS-COAL    STORAGE 


Diameter 
of  Pile 
Feet 

Total  Capacity  of  Piles,  in  Tons,  for  Depths  of 

30  Feet 

25  Feet 

20  Feet 

17^  Feet 

15  Feet 

12  Feet 

425 

63,900 

56,700 

44,800 

38,300 

31,400 

23,500 

412 

59,000 

52,400 

41,200 

35,200 

29,100 

21,500 

400 

54.700 

48,700 

38,200 

32,500 

26,800 

19,700 

387 

50,000 

44,600 

35,300 

29,800 

24,600 

17,700 

375 

46,000 

41,200 

32,300 

27,300 

22,400 

16,300 

362 

41,800 

37,400 

29,400 

24,900 

20,400 

14,600 

350 

37,700 

34,200 

27,000 

22,700 

18,400 

13,100 

337 

34,100 

30,900 

24,100 

20,400 

16,500 

1  1,  600 

325 

30,600 

27,900 

21,800 

18,300 

14,900 

IO,3OO 

312 

27,200 

24,800 

19,300 

16,300 

13,000 

300 

24,000 

22,200 

17,300 

14,300 

II,OOO 

287 

21,000 

19,600 

15,200 

12,500 

9,900 

275 

18,300 

17,200 

13,200 

10,900 

262 

15,500 

14,800 

11,400 

250 

13,200 

12,700 

10,000 

237 

10,900 

10,600 

192.  In  the  Dodge  revolving  bridge  system,  Fig.  49, 
a  light  truss  bridge  is  supported  at  one  end  on  a  pivoted 
structure  that  contains  the  operating  mechanism,  and  at  the 
other  on  a  leg  that  is  carried  by  wheels  running  on  a  cir- 
cular track.  A  clam-shell  bucket  travels  along  a  rail  sus- 
pended from  the  bridge  and  transfers  coal  from  the  cars  to 
the  pile  or  vice  versa,  every  part  of  the  storage  area  being 
reached  by  the  bucket  whether  the  pile  is  full  or  empty. 
This  system  is  used  for  storage  of  from  40,000  to  100,000 
tons  in  a  single  unit,  the  units  being  generally  rectangular 
in  form. 


130 


FUELS 


§16 


§16 


FUELS 


131 


193.  Determining  Horizontal  Pressure  Against 
Retaining  Walls. — The  horizontal  pressure  exerted,  by  any 
material,  against  retaining  walls  depends  on  the  weight  per 
cubic  foot  of  the  material,  the  depth  of  the  material  below 

TABLE   XXXI 

HORIZONTAL    PRESSURE    EXERTED    BY    ANTHRACITE 

AGyALNST  VERTICAL,    RETAINING    WALLS    PER 

FOOT    OF   LENGTH 


Horizontal 

Sloping: 

Horizontal 

Sloping 

I 

Surface 

Surface 

I 

Surface 

Surface 

s 

I 

Total 
Pressure 
Pounds 

Pressure 
Pounds 
Lowest  Foot 

Total 
Pressure 
Pounds 

Pressure 
Pounds 
Lowest  Foot 

jj 
,c 

I 

Total 
Pressure 
Pounds 

Pressure 
Pounds 
Lowest  Foot 

£  «, 

sli 

o  «  3 

"1  1 

Pressure 
Pounds 
Lowest  Foot 

I 

9.78 

9-78 

14-22 

14.22 

26 

6.611.1 

498.78 

9.612.8 

725.21 

2 

39-12 

29-34 

56.88 

42.66 

27 

7.129.5 

5i8.3S 

10.366.0 

753.67 

3 

88.02 

48.90 

127.98 

71.10 

28 

7.667.6 

537.90 

11,149.0 

782.10 

4 

156.48 

68.46 

227.52 

99-54 

29 

8,225.0 

557.46 

11.988.0 

810.54 

5 

244.50 

88.02 

355-50 

127-98 

30 

8,802.0 

577-01 

12.797.0 

839.00 

6 

352.08 

107.58 

511.92 

156.42 

31 

9,398.5 

596.59 

13.665.0 

867.41 

7 

479.22 

127.14 

606.78 

184.86 

32 

10,015.0 

616.14 

14,561.0 

895.86 

8 

62592 

146.70 

910.08 

213.30 

33 

10,650.0 

635-70 

15.486.0 

924-30 

9 

792.18 

166.26 

1.151.82 

241.74 

34 

11.306.0 

655.^6 

16,439.0 

952.70 

10 

978.00 

185.82 

1,422  JO 

270.18 

35 

11.980.0 

674.81 

17,420.0 

081.19 

i 

1.183-38 

205.38 

I.72U.62 

208.62 

36 

12.675-0 

694-39 

18,429.0 

1,009.60 

2 

1.408.32 

224.94 

2,047-68 

327.06 

37 

13,389.0 

713.94 

19.4670 

1,038.10 

3 

1,652.82 

24450 

2.403.18 

355-50 

38 

14.123.0 

733-50 

20,533.0 

1.066.50 

4 

1.916.88 

264.06 

2,787.12 

383.94 

39 

14,875.0 

753-07 

21.629.0 

1,095.00 

5 

2,200.50 

283.62 

3.199-50 

412.38 

40 

15.648.0 

772.63 

22,752.0 

1,123.40 

6 

2.503.68 

303.18 

3,640.32 

440.82 

41 

16,440.0 

792.20 

23.004.0 

1.151.80 

7 

2,826.42 

322.74 

4,109.56 

469.26 

42 

17.252.0 

811.74 

25,084.0 

1.180.30 

18 

3.168.72 

342.30 

4,607.28 

497-70 

43 

18.083.0 

830.73 

26.293.0 

1,208.70 

iQ 

3.530.58 

361.86 

5.133-42 

526.14 

44 

18.934.0 

850.86 

27,530.0 

1.237.20 

20 

3-912.00 

381.42 

5.688.00 

554.58 

45 

19.804.0 

870.41 

28.793.0 

1.265.60 

21 

4.313.00 

400.98 

6,271.00 

583.26 

46 

20.695-0 

889-99 

30,090.0 

1,294.00 

22 

4,733-50 

420.54 

6,882.50 

611.46 

47 

21,605.0 

909-54 

31,412.0 

1,322.30 

23 

5.173-70 

440.10 

7.522.50 

639.90 

48 

22,531.0 

929.10 

32,763.0 

1,350.00 

24 

5.633-30 

459-67 

8,190.70 

668.35 

49 

23,482.0 

948.66 

34.143.0 

1,379-40 

25 

6,112.60 

479-22 

8,887.50 

696.79 

50 

24.450.0 

96821 

35.550.0 

1,407.90 

NOTE.— Weight  of  anthracite  is  taken  as  52  pounds  per  cubic  foot  in  calculating 
this  table. 

the  top  of  the  wall,  or  the  line  marking  the  height  of  the 
coal  on  the  wall,  and  the  surface  of  the  pile,  whether  level  or 
sloping.  The  accompanying  formulas  and  tables  of  pressures 


132 


FUELS 


TABLE  XXXH 

HORIZONTAL,    PRESSURE    EXERTED    BY    BITTJMINOTJS    COAL, 

AGAINST    VERTICAL,    RETAINING    WALLS    PER 

FOOT    OF    LENGTH 


Horizontal 

Sloping 

Horizontal 

Sloping 

^ 

Surface 

Surface 

^ 

Surface 

Surface 

1 

8 

.5 

1|| 

Is! 

li! 

if! 

& 

s 

ft 

||| 

| 

fls 

ill 

Hi 

I 

"1 

II 

iij 

° 

|l 

**j 

JJ 

|l| 

I 

6.4 

6.4 

iol 

IO 

26 

4,305 

325 

6,760 

510 

2 

25.0 

19.0 

40 

3° 

27 

4,641 

338 

7,290 

530 

3 

57-0 

32.0 

90 

50 

28 

4,993 

350 

7,840 

550 

4 

IO2.O 

45-0 

1  60 

70 

29 

5,358 

363 

8,410 

570 

5 

159.0 

57-0 

250 

90 

30 

5,733 

376 

9,000 

590 

6 

229.O 

70.0 

360 

no 

31 

•    6,122 

389 

9,610 

610 

7 

3I2.O 

83.0 

490 

130 

32 

6,523 

401 

10,240 

630 

8 

407.0 

96.0 

640 

150 

33 

6,935 

414 

10,890 

650 

9 

516.0 

108.0 

810 

170 

34 

7,362 

427 

11,560 

670 

10 

637.0 

121.  0 

i  ,000 

190 

35 

7,778 

440 

12,250 

690 

ii 

770.0 

134.0 

I,2IO 

2IO 

36 

8,253 

452 

12,960 

710 

12 

917.0 

146.0 

1,440 

230 

37 

8,754 

465 

13,690 

730 

13 

1,076.0 

159.0 

1,690 

250 

38 

9,193 

478 

14,440 

750 

14 

1,248.0 

172.0 

1,960 

270 

39 

9,682 

490 

15,210 

770 

15 

1,433-0 

185.0 

2,250 

290 

40 

10,192 

503 

16,000 

790 

16 

1,630.0 

197.0 

2,560 

310 

4i 

10,669 

5i6 

16,810 

810 

17 

1,840.0 

210.0 

2,890 

330 

42 

11,236 

529 

17,640 

830 

18 

2,063.0 

223.0 

3,240 

350 

43 

",797 

541 

18,490 

850 

19 

2,298.0 

236.0 

3,610 

370 

44 

12,331 

554 

19,360 

870 

20 

2,548.0 

248.0 

4,000 

390 

45 

12,968 

567 

20,250 

890 

21 

2,809.0 

26l.O 

4,410 

410 

46 

13,478 

580 

21,160 

910 

22 

3,083.0 

274.0 

4,840 

430 

47 

14,100 

592 

22,090 

930 

23 

3,369-0 

287.0 

5,290 

450 

48 

14,679 

605 

23,040 

950 

24 

3,669.0 

299.0 

5,76o 

470 

49 

15,275 

618 

24,010 

970 

25 

3,981.0 

3I2.O 

6,250 

490 

50 

15,925 

631 

25,000 

990 

NOTE.- Weight  of  coal  is  taken  as  60  pounds  per  cubic  foot  in  calculating  this  table. 


FUELS  133 

for  anthracite  and  bituminous  coal  are  published  through  the 
courtesy  of  the  Link-Belt  Engineering  Company: 

For  anthracite,  let  d  represent  the  depth,  in  feet;  then 
with  surface  of  the  pile  horizontal: 
Total  pressure  in  pounds  on  wall  per  foot  of  length 

=  9.7&/1  (1) 

Pressure  on  wall  on  lowest  foot  of  depth 

=  9.78(2</-l)  (2) 

With  surface  of  pile  sloping: 
Total  pressure  in  pounds  on  wall  per  foot  of  length 

=  14.22rf*  (3) 

Pressure  on  wall  on  lowest  foot  of  depth 

=  14.22(2^-  1)  (4) 

Angle  of  repose  =  27°. 

Table  XXXI  gives  these  pressures  in  pounds  for  anthracite 
for  every  foot  of  depth  up  to  50  feet. 

For  bituminous  coal,  let  d  represent  the  depth,  in  feet,  then 
with  surface  of  pile  horizontal: 
Total  pressure  in  pounds  on  wall  per  foot  of  length 

=  6.37</'  (5) 

Pressure  on  wall  on  lowest  foot  of  depth 

=  6.37(2^-1^  (6) 

With  surface  of  pile  sloping: 
Total  pressure  in  pounds  on  wall  per  foot  of  length 

=  1(W  (7) 

Pressure  on  wall  on  lowest  foot  of  depth 

=  10(2^-1)  (8) 

Angle  of  repose  =  35°. 

Table     XXXII     gives     these    pressures    in    pounds    for 
bituminous  coal  for  every  foot  of  depth  up  to  50  feet. 


A  SERIES  OF  QUESTIONS 
AND  EXAMPLES 

RELATING  TO  THE  SUBJECTS 
TREATED  OF  IN  THIS  VOLUME 


It  will  be  noticed  that  the  Examination  Questions  con- 
tained in  the  following  pages  are  divided  into  sections 
corresponding  to  the  sections  of  the  text  of  the  preceding 
pages,  so  that  each  section  has  a  headline  which  is  the 
same  as  the  headline  of  the  section  to  which  the  questions 
refer.  No  attempt  should  be  made  to  answer  any  questions 
or  to  work  any  examples  until  the  corresponding  part  of  the 
text  has  been  carefully  studied. 


145—31 


PROPERTIES  OF  GASES 


EXAMINATION  QUESTIONS 

(1)  (a)  What  is  matter?     (b)  What  are  the  names  of 
the  three  principal  divisions  of  matter? 

(2)  Explain  what  is  meant  by  the  mass  and  the  volume 
of  a  body. 

(3)  Calculate  the  weight  of  a  cubic  yard  of  bituminous 
coal  when  the  specific  gravity  of  the  coal  is  1.3. 

Ans.  2,193.75  Ib. 

(4)  (a)  What  is  heat?     (b)  Explain  the  action  of  heat 
on  the  volume  of  a  body. 

(5)  Find  the  absolute  temperature  corresponding  to  the 
following  ordinary  temperatures:     (a)  32°  F.;     (b)   -10°C.; 
(c)  212°  F. 

(6)  What  is  the  mechanical  equivalent  of  12,000  B.  T.  U.? 

Ans.  9,336,000  ft.-lb. 

(7)  What  is  the  relation  between  the  volume  and  temper- 
ature of  gases  or  air  when  the  pressure  remains  constant? 

(8)  Calculate  the  expanded  volume  of  the  upcast  current 
in  a  furnace  shaft  where  the  temperature  of  the  air,  after 
passing  the  furnace,  is  400°  F.;  the  quantity  of  air  passing 
into  the  mine  measured  on  the  intake  airway  is  50,000  cubic 
feet  per  minute  at  a  temperature  of  32°  F.     In  making  this 
calculation,  call   the   pressure    constant,   thus  ignoring  the 

II 


2  PROPERTIES  OF  GASES  §5 

increase  of  volume  of  the  return  air  due  to  the  decrease  of 
the  pressure.  Ans.  87,400  cu.  ft.,  nearly 

(9)  When  the  reading  of  the  barometer  is  24.435  inches, 
what  is    the    atmospheric   pressure,   in  pounds   per  square 
inch?  Ans.  12  Ib.  per  sq.  in. 

(10)  Explain  what  is  meant  by  an  element  or  an  elemen- 
tary substance. 

(11)  Give  the  symbols,  molecular  weights,  and  specific 
gravities  of  the  common  mine  gases. 

(12)  What  is  the  percentage,  by  weight,  of  oxygen  in 
carbon  monoxide?  Ans.  57i  per  cent. 

(13)  (a)  Write    the   chemical    equation   expressing   the 
reaction  that  takes  place  in  the  complete  explosion  of  marsh 
gas  in  air.     (b)   Show  what  change  of  volume,  if  any,  takes 
place  at  the  moment  of  explosion. 

(14)  Calculate  the  weight  of  1  cubic  foot  of  dry  air  at  a 
temperature  of   300°   F.   and  a  barometric  pressure  of  25 
inches,  which  is  the  mean  atmospheric  pressure  at  an  eleva- 
tion of  4,800  feet  above  sea  level.  Ans.  .0436  Ib. 

(15)  How  may  the  specific  gravity  of  a  gas  be  calculated 
from  its  density? 

(16)  If   a   barometer   reads  26   inches,  what  height  of 
water  column  will    give  the  same  reading? 

Ans.  29.47  ft.,  nearly 

(17)  A  certain  mine  is  ventilated  by  an  exhaust  fan  that 
reduces  the  pressure  of  the  air  at  the  fan  14.56  pounds  per 
square  foot;  the  mine  is  situated  at  an  elevation  of  2,500  feet 
above  sea  level,  and  at  the  time  of  observation  the  reading 
of  the  barometer  was  27.286  inches.     The  measurement  of 
the  air  in  the  intake  airway  showed  a  volume  of  150,000 
cubic  feet  per  minute,  entering  the  mine  at  a  temperature  of 
40°  F.,  while  the  measurement  taken  on  the  return  airway 
showed  a  volume  of  162,700  cubic  feet  per  minute  passing 
out  of  the  mine  at  a  temperature  of  70°  F.     (a)  What  is 


§5  PROPERTIES  OF  GASES  3 

the  estimated  volume  of  gas  given  off  in  this  mine  per 
minute?  (t>)  What  is  the  percentage  of  gas  in  the  return 
air-current?  f  (a)  2,500  cu.  ft.  per  min. 

[S'\(d)  1.53+  percent. 

NOTE. — First  calculate  the  volume  of  the  air  for  the  new  tempera- 
ture and  pressure,  then  subtract  this  volume  from  the  volume  passing 
out  of  the  mine.  It  will  be  more  convenient  to  express  both  pressures 
in  pounds  per  square  foot. 

(18)  (a)  What  is  spontaneous  combustion?     (b)  How  is 
spontaneous  combustion  caused  in  coal? 

(19)  Explain  how  the  force  of  gravity  may  assist  the 
diffusion  of  gases  into  the  mine  air. 

(20)  Name     the    gases    most    commonly    occluded    in 
coal    seams. 

(21)  Which  of  the  common  mine  gases  transpires  most 
rapidly  from  the  coal? 

(22)  (a)  What  is  a  feeder  or  blower?     (6)  Explain  how 
a  gas  feeder  may  operate  to  produce  an  outburst  of  gas. 

(23)  (a)  What  is  a  gob  fire?     (b)  Describe  the  condition 
under  which  gob  fires  occur  most  frequently. 

(24)  Describe,  briefly,  the  different  methods  of  treating; 
gob  fires. 

(25)  When  it  is  necessary  to  isolate  a  mine  fire  in  order 
to  extinguish  it,  where  should  the  work  of  building  stop- 
pings be  commenced? 


MINE  GASES 


EXAMINATION  QUESTIONS 

(1)  Name  the  most  common  mine  gases,  giving  their 
symbols  and  specific  gravities. 

(2)  Which  of  the  common  mine  gases  is  the  most  deadly 
and  dangerous,  and  why? 

(3)  What  is  firedamp? 

(4)  Describe  the  effect  of  pure  marsh  gas  on  the  flame  of 
a  lamp,  and  explain  how  the  addition  of  air  to  this  gas  in 
different  proportions  changes  the  gas  with  respect  to  its 
effect  on  the  flame. 

(5)  Explain   briefly   the   effect  of   the   more   important 
mine  gases  on  firedamp. 

(6)  What  is  afterdamp,  and  how  is  the  character  of  the 
afterdamp  produced  by  the  explosion  of  a  body  of  firedamp 
affected  by  the  relative  proportions  of  the  air  and  marsh  gas 
in  the  firedamp  mixture? 

(7)  Name  the  inflammable  mine  gases. 

(8)  Name  the  principal  causes  of  the  ignition  of  gases  in 
mines. 

(9)  (a)   Explain  what  is  meant  by  an  explosive  condi- 
tion of  the  mine  air.     (b)  What  determines  the  maximum 
explosive    point   of   an  inflammable    gas?     (c)   Explain   the 
meaning  of  the  expression  "explosive  range." 

(10)  Which  of  the  common  mine  gases  has  the  widest 
explosive  range? 

It 


2  MINE  GASES  §6 

(11)  (a)   Is  an    atmosphere  in  which   lights    are  extin- 
guished necessarily  dangerous  to  life?     (b)   Is  an  atmosphere 
in  which  lights  continue  to  burn  always  safe? 

(12)  When  carbon  dioxide  is  added  to  air,  (a)  what  per- 
centage of  this  gas  is  necessary  in  the  mixture  to  extinguish 
the   flame    of   a   candle?     (b)  what   percentage  is   fatal   to 
human  life? 

(13)  What  effect  does  coal  dust  suspended  in  the   air 
have  on  the  flame  of  a  blast  or  an  explosion,  and  on  what 
does  this  effect  depend? 

(14)  (a)  What  is  a  mine  explosion?     (b)   Name  the  types 
of  mine  explosions. 

(15)  On  what  does  the  effect  of  a  gas  explosion  depend? 

(16)  What  are  the  factors  determining  the  character  of  a 
dust  explosion? 

(17)  Explain  why  an  explosion  usually  travels  against 
the  air-current. 

(18)  Explain  how  the  work  of  rescue  is  conducted  in  case 
of  a  mine  explosion. 

(19)  What  precaution  should  be  adopted  in  the  working 
of  a  mine  to  reduce  the  liability  of  an  explosion? 

(20)  Explain  the  principle  of  the  safety  lamp. 

(21)  Name  the  more  common  types  of  safety  lamps,  and 
state,  briefly,  the  conditions  or  the  work  to  which  each  is 
particularly  adapted. 

(22)  Explain    the   principal  features  of    the   Ashworth- 
Hepplewhite-Gray  safety  lamp. 

(23)  Explain  the  principal  features  of  the  Wolf  safety 
lamp. 

(24)  What  are  the  principal  forms  of  locks  for  safety 
lamps? 

(25)  Explain  the  manner  of  testing  for  gas  with  the  com- 
mon Davy  lamp  by  observing  the  height  of  the  flame  cap. 


MINE  VENTILATION 

(PART  1) 


EXAMINATION    QUESTIONS 

(1)  What  are  the  principal  means  employed  to  control 
the  direction  and  amount  of  the  air-currents  passing  through 
a  mine? 

(2)  (a)  What  is  the  purpose  of  a  mine  door  or  curtain 
in  connection    with   the   ventilation   of  a  mine?     (b)    How 
should  a  mine  door  be  built  and  how  should  it  be  hung? 

(3)  (a)  Explain  the  use  of  a  regulator  in  connection  with 
mine  ventilation,    (b)  What  two  kinds  of  regulators  are  there? 
(f)  What  effect  has  a  regulator  on  the  mine  resistance  of 
the  airway  on  which  it  is  used? 

(4)  (a)  What  is  an  air  crossing?     (b)  What  are  the  dis- 
advantages of  using  an  undercast? 

(5)  What  form  of  airway  will  give  the  most  air  with  the 
same  power  and  why? 

(6)  (a)   What     is    the    sectional     area    of    an    airway? 
(b)  What  is  the  rubbing  surface  of  an  airway?     (c)  What 
are  similar  airways? 

(7)  Find  the  perimeter,  sectional  area,  and  rubbing  sur- 
face of  an  airway  7  feet  high,  9  feet  wide,  and  1,000  feet 
long.  f  Perimeter,  32  ft. 

Ans.<Area,  63  sq.  ft. 

[Rubbing  surface,  32,000  sq.  ft. 

(8)  Explain  the  essential  difference  between  the  blowing 
or  plenum  system  of  ventilation  and  the  exhaust  system. 

us 


2  MINE  VENTILATION  §13 

(9)  What  are  the  different  factors  considered  in  connec- 
tion with  the  circulation  of  an  air-current? 

(10)  Why  is  the  quantity  of  air  passing  out  of  a  mine 
usually  greater  than  the  quantity  passing  into  the  mine  in 
the  same  period  of  time? 

(11)  When   the  velocity  of  the  current  is  300  feet  per 
minute,  what  quantity  of  air  is  passing  through  a  7'  X  T 
airway?  '  Ans.  14,700  cu.  ft.  per  min. 

(12)  (a)  What   is  meant  by  the   term  mine  resistance? 
(b)  On  what  does  the  amount  of  resistance  depend? 

(13)  (a)  What  is  meant  by  the  term   the  coefficient  of 
friction  in  mine  ventilation?     (b)   Why  does  the  value  of  the 
coefficient  of  friction  differ  under  different  conditions? 

(14)  Calculate  the  resistance  of  a  mine  airway  7  feet 
high,  8  feet  wide,  and  3,000  feet  long  when  the  velocity  of 
the  air-current  is  500  feet  per  minute.  Ans.  450  lb.« 

(15)  Explain  the  formula  p  =  —^—  and  its  application. 

a 

(16)  (a)  How  is  work  measured?     (b}  What  is  meant 
by  the  term  horsepower? 

(17)  What  power  on  the  air  is  required  to  produce  a 
velocity  of  500  feet  per  minute  in  an  airway  7  ft.  X  8  ft.  in 
section  and  3,000  feet  long?  Ans.  6.8  H.  P. 

(18)  (a)   Describe    the    common   form   of   anemometer. 
(d)  Tell  how  the  anemometer  is  used. 

(19)  (a)    Describe   the  water  gauge,     (b)    Tell  how  it 
is  used. 

(20)  What  is  the  total  ventilating  pressure  in  an  airway 
6  ft.  X  7  ft.,  the  water  gauge  being  1.5  inches? 

Ans.  327.6  Ib. 

-  (21)  What  quantity  of  air  will  a  ventilating  pressure  of 
10  pounds  per  square  foot  circulate  in  an  airway  7  ft.  X  8  ft., 
and  3,000  feet  long?  Ans.  31,235  cu.  ft. 


§13  MINE  VENTILATION  3 

(22)  What  velocity  will  15  horsepower  produce  in  an  air- 
way 7  ft.  X  8  ft.,  and  3,000  feet  long?  Ans.  650  + 

(23)  A  7'  X  10'  airway  is  passing  35,000  cubic  feet  of  air 
each  minute,  and  it  is  desired  to  reduce  this  quantity  to 
21,000  cubic  feet  each  minute  by  means  of  a  regulator.     The 
water-gauge  reading  taken  on  the  regulator  being  f  inch, 
what  must  be  the  area  of  the  opening  in  the  regulator? 

Ans.  9.2  sq.  ft. 

(24)  If  two  ventilators  producing  the  same  power  are 
used  on  the  same  airway,  will  they  produce  twice  as  much  air 
as  one  ventilator?     If  not,  how  much  more  than  one  ventila- 
tor will  the  two  ventilators  produce?    Ans.  1.26  times,  nearly. 

(25)  If  the   airways  of  a  mine  are  increased  to  double 
their  length,  other  conditions  remaining  the  same,  in  what 
proportion  would  you  have  to  increase  the  ventilating  pres- 
sure to  maintain  the  same  velocity  of  the  air  current? 

(26)  In  order  to  obtain  double  the  quantity  of  air  in  the 
same  airway,  in  what  proportion  must  the  ventilating  pres- 
sure be  increased? 

(27)  In  question  26,  in  what  proportion  would  the  power 
have  to  be  increased  to  obtain  the  same  result? 

(28)  If  you  had  the  choice  of  the  three  following  intake 
airways,  which  would  you  prefer  and  why,  all  the  airways 
being  of  the  same  length:  the  first  airway  is  8  ft.  X  8  ft.  in 
section,  the  second  6  ft..X  10  ft.,  and  the  third  5  ft.  X  10  ft? 

(29)  A  square  airway  has  a  sectional  area  of  64  square 
feet,  and  has  passing  through  it  15,000  cubic  feet  of  air  pet 
minute.     What  must  be  the  sectional  area  of  a  similar  airway 
of  equal  length  to  pass  20,000  cubic  feet  per  minute,  the 
power  remaining  the  same?  Ans.  90.25  sq.  ft. 


MINE  VENTILATION 

(PART  2) 


EXAMINATION  QUESTIONS 

(1)  What  is  meant  by  splitting  the  air  in  mine  ventila- 
tion, and  what  particular  advantage  is  gained  by  splitting? 

(2)  What  effect  does  splitting  the  air-current  in  a  mine 
have  on  the  ventilating  pressure? 

(3)  When  the  power  on  the  air  at  the  mouth  of  a  mine 
remains  unchanged  and  a  split  is  made  in  the  mine  at  a  dis- 
tance from  the  opening,  why  is  not  the  power  on  the  air  at 
the  point  of  split  the  same  after  the  split  is  made  as  it  was 
before  dividing  the  air? 

(4)  When  is  the  limit  of  splitting  the  air  reached  in  any 
section  of  a  mine? 

(5)  Name  the  chief  advantages  of  splitting  the  air-current 
in  a  mine. 

(6)  What  is  meant  by  the  natural  division  of  the  air-cur- 
rent in  mine  ventilation? 

(7)  Calculate   the  natural  division  of  an   air-current  of 
25,000  cubic  feet  between  the  following  airways:     A,  6  ft. 
X  8  ft.  and  2,000  feet  long;  Bt  8  ft.  X  12  ft.  and  3,000  feet 
long;  C,  6  ft.  X  10  ft.  and  4,000  feet  long. 

\A,  6,483  cu.  ft. 
Ans.<£,  12,526  cu.  ft. 
[C,  5,991  cu.  ft. 

(8)  Find  the  horsepower  required  to  pass  160,000  cubic 
feet  of  air  per  minute  in  four  equal  splits.     The  size  of  all 

114 


2  MINE  VENTILATION  §14 

the  airways  is  8  ft.  X  10  ft.,  and  the  length  of  each  split, 
including  the  return,  is  3,000  feet.  Ans.  32.728  H.  P. 

(9)  Find  the  unit  of  ventilating  pressure   that  will  be 
required  to  circulate  50,000  cubic  feet  of  air  per  minute  in 
two  equal  splits,  each  split  being  6  ft.  X  8  ft.  and  6,000  feet 
long,  including  the  return.  Ans.  19  Ib.  per  sq.  ft. 

(10)  (a)   Find  the  unit  of  ventilating  pressure  that  will 
circulate  150,000  cubic  feet  of  air  per  minute  in  the  following 
three  unequal   splits,  starting  from   the  same  point  in  the 
mine:    A,  8  ft.  X  10  ft.  and  3,000  feet  long;  B,  6  ft.  X  12  ft. 
and   4,000  feet  long;   C,  8  ft.  X  8  ft.   and  2,000  feet   long. 
(6)  What  is  the  horsepower  on  the  air  at  the  point  where 
the  air-current  is  divided?          .        f  (a)  13.326  Ib.  per  sq.  ft. 

IS'1(£)  60.57  H.  P. 

(11)  Suppose   that  50,000  cubic  feet  of  air  per  minute 
passes  through  an  airway  10  ft.  X  10  ft.  and  10,000  feet  long, 
and  that  a  change  is  made  by  dividing  the  current  into  three 
splits  of  the  following  dimensions:   A,  6  ft.  X  6  ft.  and  4,000 
feet  long;  B,  5  ft.  X  6  ft.  and  3,000  feet  long;  C,  5  ft.  X  5  ft. 
and  4,000  feet  long,     (a)  What  quantity  will  pass  through 
each  of  the  splits  that  are  now  substituted  for  the  original 
airway,  assuming  that  the  total  quantity  remains  the  same? 
(6)  What  horsepower  is  required  to  pass  the  given  quantity 
of  air  in  a  single  current?     (<:)   What  horsepower  will  circu- 
late the  given  quantity  in  the  three  splits? 

(A,  19,597  cu.  ft.  per  min. 
B,  17,980  cu.  ft.  per  min. 
C,  12,423  cu.  ft.  per  min. 

(t>)  30.3  H.  P. 
(g)  23.94  H.  P. 

(12)  A  slope  mine  is  ventilated  by  means  of  an  air-shaft, 
which  forms  the  upcast  shaft  for  sections  A  and  B.     The 
main  intake  for  the  entire  mine  is  the  haulage  slope.    At  the 
foot  of   the   slope,   the  entire  intake  current   is  conducted 
through  a  single  main  airway  for  a  distance  of  1,500  feet  to 
a  point  where  it  is  divided  into  two  currents,  each  current 
ventilating  a  separate  section  of  the  mine  after  which  they 


§  14  MINE  VENTILATION  3 

pass  out  through  a  common  upcast  shaft.  The  sizes  of  the 
slope,  airways,  and  shaft  are  as  follows:  Haulage  slope,  6  ft. 
X  12  ft.  and  2,000  feet  long;  main  intake  airway,  10  ft.  X  12  ft. 
and  1,500  feet  long;  split  A,  8  ft.  X  12  ft.  and  6,000  feet  long; 
split  B,  8  ft.  X  10  ft.  and  4,000  feet  long;  upcast  shaft,  10  ft. 
X  10  ft.  and  500  feet  deep,  (a)  Find  the  unit  of  ventilating 
pressure  that  will  circulate  100,000  cubic  feet  of  air  in  this 
mine,  (b)  Find  the  total  horsepower  producing  the  circula- 
tion in  this  mine.  *  o  /(a)  64  Ib.  per  sq.  ft. 

^"••U*)  194  H.  P. 

(13)  Explain  briefly  the  essential  factors  that  determine 
the  efficient  ventilation  of  a  mine. 

(14)  Name  one  of  the  principal  features  in  the  ventila- 
tion of  inclined  seams. 

(15)  What  is  an  air  column  in  mine  ventilation? 

(16)  What  is  meant  by  the  term  motive  column  as  used 
in  mine  ventilation? 

(17)  A  certain  mine  is  ventilated  by  two  shafts,  each 
being  600  feet  deep;  the  average  temperature  of  the  furnace 
shaft  is  380°  F.,  while  that  of  the  downcast  shaft  is  40°  F, 
(a)  What  is  the  height  of  the  motive  column,  in  terms  of  the 
downcast  air?     (b)  What  pressure  and  water  gauge  does  this 
column  represent? 

{(a)  243ft. 
s-\(£)  19.352  Ib.  persq.  ft.,  or  3.72  in.  water  gauge. 

(18)  Which  are  the  most  difficult  to  ventilate,  rise  or 
dip  workings  and  why? 

(19)  In  furnace  ventilation,  what  determines  the  weight 
of  coal  burned  per  hour,  and  how  is  this  weight  of  coal 
calculated? 

(20)  In  a  mine  ventilated   by  a  furnace,   a  current   of 
60,000  cubic  feet  of  air  is  passing;  the  depth  of  the  furnace 
shaft  is  200  feet.      Other  conditions  remaining  unchanged, 
what  quantity  of  air  will  be  circulated  in  this  mine  if  a  stack 
40  feet  in  height  is  erected  over  the  mouth  of  the  upcast  or 
furnace  shaft?  Ans.  65,700  cu.  ft.  per  min. 


MINE  VENTILATION 

(PART  3) 


EXAMINATION   QUESTIONS 

(1)  (a)  Into  what  two  general  classes  may  ventilating 
fans  be  divided  with  respect  to  their  principle  of  action? 
(£)   Into  what  two  classes  may  centrifugal  fans  be  divided 
with  respect  to  the  manner  of  discharging  the  air  from  the 
fan? 

(2)  What  points  should  be  mentioned  in  describing  a 

centrifugal  fan? 

(3)  Explain  the  principle  of  the  action  of  the  centrifugal 
fan. 

(4)  Explain  in  what  way  an  exhaust  fan  differs  from  a 
blower  fan  with  respect  to  its  connection  with  the  mine. 

(5)  (a)   Explain  what  is  meant  by  the  fan  housing  and 
what    is   its  purpose,     (b)   Where   should  the   expansion  of 
the  fan  casing  begin,  and  why  should  the  fan  casing  expand 
uniformly  around  the  fan? 

(6)  Explain  briefly  how  the  spiral  of  a  fan  is  laid  out. 

(7)  Mention  some  of  the  chief  causes  of  vibration  in  a 
centrifugal  fan  and  state  what  means  may  be  taken  to  reduce 
or  prevent  such  vibration. 

(8)  Explain  briefly  how  the  air-current  in  a  mine  venti- 
lated by  a  centrifugal  fan  can  be  reversed. 

(9)  Describe,  in  a  few  words,  the  general  features  of  the 
Nasmyth  fan. 

115 

145—3? 


2  MINE  VENTILATION  §15 

(10)  How  does   the  Guibal   fan   differ   in   its   principal 
features  from  the  Nasmyth  fan? 

(11)  (a)    What    are    the    chief    characteristics    of    the 
Waddle  fan?     (b)  How  does   the  Schiele   fan  differ   from 
the   Waddle   fan? 

(12)  (a)   Calculate  the  diameter  of  the  central  orifice  or 
intake  opening  of  a  single-intake  fan  designed  to  pass  150,000 
cubic  feet  of  air  per  minute,     (b)   Find  the  inner  diameter 
for  a  double-intake  fan  that  will  pass  the  same  quantity  of  air. 

(13)  (a)  What  forms  the  basis  for  calculating  the  size  of 
the  intake  opening  of  a  fan?     (b}   Explain  what  consideration 
determines  the  breadth  of  a  fan  with  respect  to  the  diameter 
of  its  intake  opening. 

(14)  (a)  Find  the  volume  of  a  fan  whose  outer  and  inner 
diameters  are  16  feet  and  10  feet,  respectively,  and  whose 
breadth  is  4  feet  6  inches,     (b)  Assuming  the  weight  of 
1  cubic  foot  of  air  within  the  fan  to  be  .083  pound,  find 
the  weight  of  the  revolved  air  and  its  centrifugal  force  when 
the  fan  is  making  100  revolutions  per  minute,     (c)  Assuming 
a  mine  resistance  of  pa  —  800  pounds  and  an  efficiency  of 
the  ventilator  of  K  =  .60,  find  the  acceleration  due  to  the 
action  of  this  fan  at  the  given  speed  and  the  quantity  of  air 
that  will  be  produced  under  these  conditions. 

(a)  551+  cu.  ft. 

(b)  Weight  =  45.7+  lb.; 


Ans. 


Centrifugal  force  =  1,023  lb. 


(c)  Acceleration  =  24.8+  ft.  per  sec.; 
Quantity  =  68,800  cu.  ft.  per  min. 

(15)  (a)  Calculate  the  size  of  fan  required  to  circulate 
190,000  cubic  feet  of  air  against  a  pressure  of  3.32  pounds 
per  square  foot,  at  a  speed  of  100  revolutions  per  minute, 
the  area  of  the  fan  drift  where  the  quantity  and  pressure 
are  measured  being  as  in  question  14,  a  =  120  square  feet, 
using  the  formula  given  in  Art.  35  to  calculate  the  outer 
diameter  of  the  fan.  (b}  Calculate  the  size  of  a  double- 
intake  fan  that  will  circulate  68,800  cubic  feet  of  air  per 
minute  against  a  pressure  of  6.67  pounds  per  square  foot,  at 


§  15  MINE  VENTILATION  3 

a  speed  of  100  revolutions  per  minute,  these  being  the  con- 
ditions for  the  fan  in  question  14. 

(a)   Inner  diameter  d  =  10  ft.; 
Outer  diameter  D  =  16  ft.; 
.        ,         Breadth  =  6  ft.  3  in. 
Ans'<(£)  d   =  6ft. 

b    =  3  ft.  9  in. 
D  =  14  ft.  1  in. 

(16)  Find  the  horsepower  that  will  be  required  to  operate 
the   fan  in   question  14,  assuming   its   efficiency   to   be,  as 
stated,  60  per  cent. 

(17)  Find  the  horsepower  necessary  to  drive  the  fans  in 
question  15  (a)  and  (b}. 

(18)  If  the  velocity  of  the  air  in  the  fan  drift  where  the 
pressure  is  measured  is  30  feet  per  second  and  the  water 
gauge  produced  by  the  fan  is  2.4  inches,  what  static  gauge 
would  this  fan  produce  at  the  same  speed;  or,  in  other  words, 
what  would  be  the  water  gauge  produced  by  this  fan  at  the 
same  speed  if  the  fan  drift  were  closed  tightly,  so  that  no 
air  could  pass  through  the  fan?  Ans.  5.14+  in. 

(19)  (a)  Theoretically,  what  should  the  term  mechanical 
efficiency  of  a  fan  mean?     (b}  Why  is  not  this  its  meaning 
in  the  usual  method  of  making  a  fan  test? 

(20)  (a)  What  observations  are  necessary  to  be  taken  in 
determining  the  mechanical  efficiency  of  a  fan?     (b)  Explain 
briefly  the  important  points  to  be  observed  in  making  a  test 
of  the  efficiency  of  a  fan. 


FUELS 


EXAMINATION   QUESTIONS 

(1)  What  is  meant  by:   (a)  proximate  analysis?    (b)  ulti- 
mate analysis? 

(2)  What  is  the  amount  of  available  hydrogen  in  a  coal 
analyzing,  moisture  10.34  per  cent.,  carbon  74.37  per  cent., 
hydrogen  2.58  per  cent.,   oxygen  8.72  per  cent.,  nitrogen 
1.76  per  cent.,  sulphur  .73  per  cent.,  ash  1.5  per  cent.? 

(3)  What  is  the  percentage  of  carbon  and  volatile  matter 
in  the  combustible  of  a  coal  analyzing,  moisture  3.5  per  cent., 
fixed  carbon  57.3  per  cent.,  volatile  matter  36.3  per  cent., 
ash  2.9  per  cent.,  sulphur  1.15  per  cent.? 

(4)  What  requirements  should  be    fulfilled   by  a    good 
steaming  coal? 

(5)  Why  does  not  the  calorific  power  of  a  coal  express 
correctly  its  heating  value  for  steaming  purposes? 

(6)  'Under  what  conditions  can  a  chemical  analysis  of 
coal  be  relied  on  as  a  check   in   determining  the  relative 
values  of  different  coals  for  a  given  purpose? 

(7)  What  items  determine  largely  the  market  price  of 
coal? 

(8)  (a)  What  causes  lead  to  the  spontaneous  combustion 
of  coal?     (b)  Under  what  conditions  is  spontaneous  combus- 
tion most  liable  to  occur? 

(9)  How  is  coal  dust  used  as  a  fuel? 

(10)  Mention  briefly  the  advantages  and  disadvantages 
of  petroleum  as  a  fuel. 

116 


2  FUELS  §  16 

(11)  How  is  petroleum   burned   in   a   furnace  under  a 
boiler? 

(12)  What  are  the  principal  kinds  of  gases  used  as  fuel? 

(13)  What  are  the  principal  chemical  reactions  that  take 
place  when  a  fuel  containing  carbon  and  hydrogen  is  burned 
in  excess  of  air? 

(14)  Calculate  the  weight  of  air  theoretically  necessary 
for  the  complete  combustion  of  1  pound  of  coal  whose  analy- 
sis is,  water  .73  per  cent.,  carbon  91.4  per  cent.,  hydrogen 
2.59  per  cent.,  oxygen  .08  per  cent.,  nitrogen  .21  per  cent., 
sulphur  .21  per  cent.,  ash  3.04  per  cent. 

(15)  Define  the  terms  temperature  of  ignition  and  tem- 
perature of  the  fire. 

(16)  What  will  be  the  theoretical  temperature  of  the  fire, 
that  of  the  atmosphere  being  75°  F.,  in  burning  a  coal  ana- 
lyzing, moisture  .69  per  cent.,  carbon  81.15  per  cent.,  hydro- 
gen 5.21  per  cent.,  oxygen  2.24  per  cent.,  nitrogen  1.3  per 
cent.,  sulphur  .68  per  cent.,  ash  8.73  per  cent.?     The  sulphur 
and  ash  need  not  be  taken  into  account.      The  dry  gases 
amount  to  19.8  pounds  per  pound  of  combustible. 

(17)  How  many  pounds  of  air  are  supplied  in  burning 
1  ton  (2,000  pounds)  of  a  coal  analyzing  76  per  cent,  carbon, 
if    the    gases    have    the    composition    (by  volume),  carbon 
dioxide  11.5  per  cent.,  carbon  monoxide  .9  per  cent.,  oxygen 
7.4  per  cent.,  nitrogen  80.2  per  cent.? 

(18)  Calculate,  by  Dulong's  formula,  the  heating  value 
of  a  coal  having  the  composition,  water  .73  per  cent.,  carbon 
82.89  per  cent.,  hydrogen  4.53  per  cent.,  oxygen  .4  percent., 
nitrogen  .64  per  cent.,  sulphur  .68  per  cent.,  ash  10.13  per 
cent. 

(19)  Calculate,  by  Lord  and  Haas's  formula,  the  heating 
value  of  a  Pocahontas  coal  having  the  following  proximate 
analysis:    Moisture  1.5  per  cent.,  volatile  matter  21  per  cent., 
fixed  carbon   74.39   per  cent.,  ash  3.11   per  cent.,  sulphur 
.58  per  cent. 


§  16  FUELS  3 

(20)  What  will  be  the  loss  of  heat  due  to  hydrogen  and 
moisture  in  burning  1  pound  of  a  coal  having  the  composi- 
tion, moisture  .69  per  Cent.,  carbon  81.15  per  cent.,  hydrogen 
5.21  per  cent.,  oxygen  2.24  per  cent.,  nitrogen  1.3  per  cent., 
sulphur  .68  per  cent.,  ash  8.73  per  cent.,  the  temperature  of 
the  atmosphere  being  70°  F.  and  that  of  the  gases  580°  F.? 

(21)  What  are  the  principal  means  of  handling  coal  in 
large  quantities? 

'(22)     Why  is  it  necessary  to  store  coal? 


A  KEY  TO  ALL  THE  QUESTIONS 
AND  EXAMPLES 

INCLUDED  IN  THE  EXAMINATION  QUESTIONS 


It  will  be  noticed  that  the  Keys  have  been  given  the  same 
section  numbers  as  occur  on  the  headlines  of  Examination 
Questions  to  which  they  refer.  All  article  references  refer 
to  the  Instruction  Paper  bearing  the  same  section  number 
as  the  Key  in  which  it  occurs,  unless  the  title  of  some  other 
Instruction  Paper  is  given  in  connection  with  the  article 
number. 

To  be  of  the  greatest  benefit,  the  Keys  should  be  used 
sparingly.  They  should  be  used  much  in  the  same  manner 
as  a  pupil  would  go  to  a  teacher  for  instruction  with  regard 
to  answering  some  example  he  was  unable  to  solve.  If  used 
in  this  manner,  the  Keys  will  be  of  great  help  and  assist- 
ance to  the  student,  and  will  be  a  source  of  encouragement 
to  him  in  studying  the  various  papers  composing  the  Course. 


PROPERTIES  OF  GASES 


(1)  (a)  and  (*)  See  Art.  1. 

(2)  See  Art.  3. 

(3)  Substituting  the  given  values  in  the  formula  given  in  Art.  8, 
we  have  for  the  weight  of  a  cubic  foot  of  this  coal,  w  =  62.5  X  1.3 
=  81.25  Ib.     Then,  since  there  is  27  cu.  ft.  in  a  cubic  yard,  the  weight 
of  a  cubic  yard  of  the  coal  is  w  =  27  X  81.25  =  2,193.75  Ib.    Ans. 

(4)  (a)  See  Art.  22. 

(b)  The  effect  of  heat  is  to  drive  the  molecules  of  a  body  farther 
apart  and  thus  cause  an  increase  in  the  volume  of  the  body. 

(5)  (a)   r=460+    32  =  492°  P.,  absolute.     Ans. 

(b)  T  =  273  -    10  =  263°  C.,  absolute.     Ans. 

(c)  T  =  460  +  212  =  672°  P.,  absolute.     Ans. 

V6)    As  explained  in  Art.  36,  12,000  X  778  =  9,336,000  ft.-lb.    Ans. 

(7)  When    the    pressure  of  a  gas  remains   constant,   the  volume 
increases  or  decreases  in  the  same  proportion  as  the  absolute  tempera- 
ture increases  or  decreases. 

(8)  Applying  the  formula  of  Art.  52, 

••  near!-  Ans- 


(9)  From  Art.  57,  p  =  .4911  X  24.435  =  12  Ib.  per  sq.  in.     Ans. 

(10)  See  Art.  69. 

(11)  The  symbols  and  molecular  weights  of   the  common  mine 
gases  are  given  in  Table  IX.     The  specific  gravities  of  these  gases  are 
given  in  Table  XII. 

(12)  The   chemical    symbol    for   carbon    monoxide    is    CO.     The 
atomic  weights  of  the  elements  forming  a  molecule  of  this  gas  are 

Carbon,  C  ......................  12 

Oxygen,  O  ......................  16 

Molecular  weight,  carbon  monoxide  .........  28 

II 


2  PROPERTIES  OF  GASES  §5 

1  fi 

The  percentage,  by  weight,  of  the  oxygen  in  the  gas  is  then  ^  X  100 

Zo 

=  57|  per  cent.    Ans. 

(13)  (a)  The  chemical  equation  expressing  the  reaction  that  takes 
place  in  the  complete  explosion  of  marsh  gas  in  air,  together  with  the 
molecular  volume  of  each  of  the  gases  before  and  after  explosion  is 
(See  Art.  88) 

CH<  +  2O,  +  8JV,  =  CO,  +  2H3O  +  8N, 
Molecular  volume  1  28     =     1  2  8 

(t>)     It  is  readily  observed  that  there  are  eleven  volumes  before  and 
after  explosion,  and  hence,  no  change  of  volume  occurs  in  this  case. 

(14)  Substituting  the  given  values  in  the  formula  given  in  Art.  91, 

1  327^  V  *?*} 
the  weight  of  1  cu.  ft.  of  air  under  these  conditions,  w  =  -^ 

4oU  ~f~  oUO 
=  .0436+  Ib.    Ans. 

(15)  By  dividing  the  density  of  the  gas  referred  to  hydrogen  by  the 
density  of  air  referred  to  hydrogen,  namely  14.4.     See  Art.  93. 

(16)  See  Art.  55.     ?*L*JM  =  29.47  ft.,  nearly.     Ans. 

(17)  (a)     In  this  case,  the  volume  of  the  return  air-current  is  not 
only  increased    by  the    gases   given  off  in  the  mine,  but  the  air  is 
expanded  and  its  volume  increased  both  by  the  increase  of  tempera- 
ture and  the  decrease  of  pressure.     The  expanded  volume  due  to  these 
causes  must  first  be  calculated.     When  the  reading  of  the  barometer 
is  27.286  in.,  the  atmospheric  pressure  is  27.286  X  .4911  =  13.400  Ib. 
per  sq.  in.,  or  144  X  13.4  =  1,929.6  Ib.  per  sq.  ft.     The  absolute  pres- 
sure in  the  intake  is  the  atmospheric  pressure  1,929.6  Ib.  per  sq.  ft., 
while  the  absolute  pressure  on  the  return,  when  the  fan  is  exhaust- 
ing, is  1,929.6  -  14.56  =  1,915.04,  say  1,915  Ib.  per  sq.  ft.     Applying 
formula  2, 

Art.  e.,  „  .  ,  (££) 

cu.  ft.  per  min.,  nearly.  Since  the  measurement  of  the  return  air  has 
shown  a  volume  of  162,700  cu.  ft.  per  min.,  the  volume  of  gas  in  this 
current  may  be  assumed  as  162,700  -  160,200  =  2,500  cu.  ft.  per  min. 

Ans. 

(b)     The   percentage  of   gas  in   this   current   is   then   — ^yr^  -„- — 
=  1.53+  per  cent.    Ans. 

(18)  (a)  and  (£)  See  Art.  1O6. 

(19)  When  a  gas  lighter  than  air  issues  from  the  floor  of  the  mine, 
the   tendency   of   the    gas   to  rise    causes   it   to   mix   freely  with   the 


§5  PROPERTIES  OF  GASES  3 

air-current  and  thus  increase  the  surface  of  contact  of   the  gas  with 
the  air,  which  increases  the  rate  of  diffusion.     See  Art.  1O8. 

(20)  See  Art.  111. 

(21)  The  hydrocarbon  gases,  methane  and  ethylene  gas,  transpire 
more  rapidly  than  the  other  mine  gases  (Table  XV).     See  Art.  114. 

(22)  (a)  See  Art.  115. 

((>)  The  extraction  of  the  coal  breaks  the  roof  and  in  some  cases 
crevices  the  coal,  thus  allowing  the  gas  from  a  pocket  or  feeder  to 
become  distributed  over  a  large  area  of  the  coal  face  or  the  rib  of  an 
entry  or  chamber.-  If  the  coal  gives  way  under  this  great  pressure,  an 
outburst  of  gas  is  the  result.  See  Art.  116. 

(23)  (a)  Art.  117.     A  gob  fire  is  a  fire  occurring  in  the  waste 
material  in  the  mine  workings. 

[b)  Gob  fires  occur  most  frequently  under  moist  conditions  and 
where  the  ventilation  is  sluggish,  and  where  the  refuse  is  fine. 

(24)  A  small  fire  that  just  started  or  is  easily  accessible  should  be 
loaded  out  before  it  can  spread  over  a  considerable  area;  no  trace  of  it 
should  be  allowed  to  remain.     The  place  should  then  be  thoroughly 
ventilated  (Art.  119).     When  gas  feeders  have  been  ignited  and  con- 
tinue to  burn  under  the  waste  or  in  any  other  inaccessible  place,  the 
flames  should  be  extinguished,  if  possible,  by  exploding  a  small  stick 
of  dynamite  near  the  place  (Art.  12O).     Where  the  fire  has  spread 
over  a  considerable  area,   it  may   become   necessary  to  seal  off  the 
portion  of  the  workings  affected  by  the  fire  so  as  to  smother  the  same. 
This  is  accomplished  by  building  air-tight  stoppings  in  all  the  open- 
ings leading  to  this  portion  of  the  mine.     The  place  must  remain 
closed  for  a  sufficient  period  of  time  for  the  fire  to  be  completely 
extinguished  (Art.   121).     Culm  is  often  used  in  anthracite  mines  to 
fill  the  places  surrounding  a  fire  so  as  to  shut  off  the  air  and  smother 
the  fire.     The  culm  is  mixed  with  water  and  run  into  the  mine  after 
temporary  stoppings  have  been  erected  at  the  mouths  of  all  places  to 
be  filled  (Art.  122).     When  all  other  methods  have  failed  to  extin- 
guish the  fire,  a  mine  may  be  flooded,  as  a  last  resort  (Art.  123). 

(25)  The  work  of  building  stoppings  should  be  commenced  at  the 
return  end  of  the  district  to  be  shut  off,  and  should  proceed  in  order 
toward  the  intake  opening,  which  should  be  closed  last.     See  Art.  121. 


MINE  GASES 


(1)  See  Table  I. 

(2)  Carbon  monoxide;  because  the  gas  is  very  poisonous  and  in 
it  the  lamps  continue  to  burn  even  more  brightly  than  in  air;  the  pres- 
ence of  the  gas  is,  therefore,  unsuspected  by  the  miner.     See  Art.  3. 

(3)  Any  explosive  mixture  of  marsh  gas  and  air.     See  Art.  12. 

(4)  Pure  marsh  gas  will  extinguish  the  flame  of  a  lamp  because 
this  gas  does  not  support  combustion.     The  addition  of  air  to  the  gas 
permits   lamps  to   burn  in   the   mixture.     As   the   quantity  of  air  is 
increased,  the  flame  is  more  and  more  disturbed,  and  when  the  gas 
and  air  are  mixed  in  the  proportion  of  one  volume  of  gas  to  five  vol- 
umes of  air,  the  mixture  becomes  slightly  explosive.     As  the  quantity  of 
air  is   further   increased,   the    explosiveness   is  increased,  reaching  a 
maximum  when  the  proportion  of  gas  to  air  is  1  :  9.66.     Beyond  this 
point,  as  the  quantity  of  air  is  still  increased,  the  explosive  force  is 
decreased  until  it  ceases  altogether  when  the  proportion  of  gas  and  air 
is  1  :  13.     When  the  proportion  reaches  1  :  16,  the  flame  is  voluminous 
or  enlarged  and  very  much  disturbed.     Larger  proportions  of  air  than 
this  are  manifested  by  the  formation  of  a  pale-blue  flame  cap  sur- 
mounting the  flame  of  the  lamp.     The  height  of  this  flame  cap  decreases 
as  the  proportion  of  air  is  increased,  and  ceases  to  be  visible  when  the 
proportion  of  gas  and  air  is  1  :  40. 

(5)  The  effect  of  carbon  dioxide  on  firedamp  is  to  decrease  the 
explosiveness  of  the  mixture.     Likewise,  the  effect  of  nitrogen  is  to 
dilute  the  gases  and  weaken  the  explosive  force  of  the  mixture.    When 
the  firedamp  is  at  its  most  explosive  point,  the  addition  of  one-seventh 
of  its  volume  of  carbon  dioxide  or  one-sixth  of  its  volume  of  nitrogen 
will  render  the  firedamp  inexplosive.      Carbon  monoxide  mixed  with 
firedamp  widens  the  explosive  range  of  the  gas.  'Olefiant  gas  renders 
the  firedamp  mixture  more  easily  ignitible  and  increases  its  explosive 
force. 

(6)  Afterdamp  is  a  mixture  of  gaseous  products  resulting  from  a 
mine  explosion.     When  the  firedamp  is  at  its  most  explosive  point,  the 
afterdamp  of  the  explosion  consists  of  carbon  dioxide,  CO,,  and  water, 
HtO,  together  with  the  nitrogen  remaining  from  the  air  concerned  in 

M 


2  MINE  GASES  §6 

the  explosion.  When  the  firedamp  contains  an  insufficient  quantity  of 
air  for  the  complete  combustion  of  the  marsh  gas,  the  afterdamp  pro- 
duced by  the  explosion  consists  of  carbon  dioxide,  CO,,  carbon  mon- 
oxide, CO,  water,  HtO,  and  free  hydrogen,  H.  See  Art.  18. 

(7)  Marsh  gas,  C7/4,  carbon  monoxide  or  whitedamp,  CO,  hydro- 
gen sulphide,  HtS.     See  Art.  19. 

(8)  The  flame  of  a  naked  lamp  or  match  or  a  defective  safety 
lamp,  the  flame  resulting  from  blasting,  the  sparking  or  incandescence 
of  electric  wires,  and  mine  fires.     See  Art.  22. 

(9)  (a)     An  explosive  condition  of  the  mine  air  exists  when  the  air 
contains  a  certain  proportion  of  inflammable  gas. 

(b)  For  each  inflammable  gas,  there  is  a  certain  proportion  of  air 
required  for  its  complete  combustion,  and  this  proportion  determines 
the  maximum  explosive  point  for  such  gas. 

(c)  As  the  proportion  of  air  required  for  the  complete  combustion 
of  the  gas  is  increased  or  decreased,  the  explosiveness  of  the  mixture 
decreases  and  ceases  altogether  at  points  above  and  below  the  maxi- 
mum explosive  point,  which  points  are  called  the  explosive  limits  of 
the  gas.     These  two  limits  determine  the  explosive  range  of  the  gas, 
and  any  proportion  of  air  and  gas  lying  within  this  range  is  explosive. 
See  Art.  25. 

(10)  Carbon  monoxide,  CO,  whose  lower  explosive  limit  is  1  :  13  and 
whose  higher  limit  is  1  :  75,  has  the  widest  explosive  range  of  any  of 
the  common  mine  gases.     (See  Table  IV.)     Hydrogen  gas  has  a  slightly 
greater  range  than  this,  but  it  does  not  occur  commonly  or  abundantly 
as  a  mine  gas. 

(11)  (a)  Lights  are  often  extinguished  in  an  atmosphere  that  may 
be  breathed  for  a  considerable  time  without  serious  injury. 

(b)     Lights  often  continue  to  burn  brightly  in  the  presence  of  poi- 
sonous gases  that  will  produce  death  in  a  short  time.     See  Art.  26. 

(12)  (a)  A  candle  is  extinguished  by  an  artificial  atmosphere  con- 
taining 14  per  cent,  of  carbon  dioxide.     See  Table  VII. 

(b)     An  atmosphere  becomes  fatal  to  life  when  it  contains  18  per 
cent,  of  carbon  dioxide.     See  Table  V. 

(13)  A  dry  and  dusty  atmosphere  lengthens  the  flame  of  a  lamp  or 
the  flame  of  a  blast.     This  effect  is  in  proportion  to  the  fineness  and 
inflammability  of  the  dust,  the  presence  of  small  quantities  of  gas  in  the 
air,  and  the  volume  and  intensity  of  the  flame.     See  Art.  3O. 

(14)  See  Art.  31. 

(15)  The    relative    size    of   the    workings    and    the    body    of    gas 
exploded,  the  degree  of  explosiveness  of  the  firedamp  mixture  and  the 
temperature  and  velocity  of  the  air  in  circulation.     See  Art.  32. 


§6  MINE  GASES  3 

(16)  The  fineness  and  inflammability  of  the  dust  and  its  free  suspen- 
sion in  the  air,  and  the  volume  and  intensity  of  the  flame  causing 
ignition.     See  Art.  33. 

(17)  The  intake  airway  furnishes  a  plentiful  supply  of  fresh  air, 
which  is  necessary  to  support  the  flame.     See  Art.  38. 

(18)  See  Art.  41. 

(19)  See  Art.  45. 

(20)  See  Art.  47. 

^21)  The  Davy  lamp  is  adapted  to  testing  for  gas  because  of  its 
free  admission  of  air  through  the  gauze  of  the  lamp.  (See  Art.  54.) 
The  Clanny  lamp  is  not  a  good  lamp  for  testing  for  gas,  but  when  bon- 
neted is  well  adapted  to  general  work  in  the  mine.  (See  Arts.  56  and 
57.)  The  bonneted  Mueseler  lamp  is  adapted  to  gaseous  mines, 
owing  to  the  sheet-iron  conical  chimney  within  the  lamp  increasing  its 
security  against  explosion.  This  lamp,  however,  is  easily  extinguished 
when  turned  on  one  side.  (See  Arts.  6O  and  61.)  The  Marsaut  lamp 
is  adapted  to  general  work  in  strong  air-currents,  owing  to  the  pro- 
tection afforded  in  this  lamp  by  the  multiple  gauze  chimneys. 
See  Art.  62. 

(22)  This  lamp  may  be  arranged  to  draw  its  air  from  above  the 
lamp  through  the  standards,  which  are  hollow  tubes.     By  this  means, 
a  thin  layer  of  gas  at  the  roof  may  be  tested  without  tilting  the  lamp. 
The  conical  glass  chimney  assists  the  upward  diffusion  of  the  light,  thus 
permitting  a  better  inspection  of  the  roof.     The  gauze  is  conical,  but 
small  in  size.     See  Art.  65. 

(23)  See  Art.  66. 

(24)  The  simple  screw  pin  is  used  in  many  lamps,  but  is  unsafe 
because  it  is  easily  opened.     (See  Art.  7O.)     The  common  lead-plug 
lock  cannot  be  opened  without  this  being  detected.     (See  Art.  71.) 
The  spring  lock  of  lamps  of  the  protector  type  cannot  be  opened  without 
extinguishing  the  light.     (See  Art.  72.)     Magnetic  locks  can  only  be 
opened  by  the  use  of  a  strong  magnet  in  the  lamp  room.     See  Art.  73. 

(25)  The  flame  of  the  lamp  is  first  drawn  down  to  a  small  glimmer. 
The  lamp  is  raised  slowly  in  an  upright  position  into  the  body  of  gas 
and  the  flame  carefully  watched  for  the  first  appearance  of  a  cap,  the 
observer  screening  his  eyes  with  his  hand  from  the  bright  portion  of 
the  flame.     The  height  of  the  cap  is  observed  before  the  voluminous 
flame  indicates  the  percentage  of  gas  present.     See  Art.  86. 


145—33 


MINE  VENTILATION 

(PART  1) 

(1)  See  Art.  2. 

(2)  (a)  See  Arts.  3  and  4. 

(b)  See  Art.  3. 

(3)  (a)  Its  use  is  to  regulate  or  control  the  amount  of  air  passing 
through  the  airway.     By  the  use  of  one  or  more  regulators,  the  air  is 
divided  between  the  several  districts  of  the  mine  in  proportion  to  the 
requirements  in  each  district.     See  Art.  5. 

(b)  See  Art.  5. 

(c)  It  has  the  same  effect  as  increasing  the  length  of  the  airway, 
and  therefore  increases  the  resistance  of  the  airway.     See  Art.  42. 

(4)  (a)  and  (b)  See  Art.  8. 

(5)  The  circular  airway;  because  it  has  the  smallest  perimeter  and 
therefore  the  smallest  rubbing  surface  for  the  same  sectional  area  of 
the  airway.     See  Art.  1O. 

(6)  (a)  and  (6)  See  Art.  9. 

(c)  See  Art.  11. 

(7)  The  perimeter  is  o  =  2(7  +  9)  =  32  ft.     The  sectional  area  is 
a  =  7  X  9  =  63  sq.  ft.     The  rubbing  surface  is  s  =  1,000  X  32  =  32,000 
sq.  ft.     Ans.     See  Art.  9. 

(8)  See  Art.  14. 

(9)  The  power  producing  the  circulation  is  the  producing  factor. 
The  resisting  factors  are  the  rubbing  surface  and  the  unit  of  resist- 
ance.    The  resulting  factors  are  the  velocity,  quantity,  and  pressure 
of  the  air  and  the  work  performed  in  moving  the  air-current.     See 
Art.  15. 

(10)  See  Art.  16. 

(11)  The  sectional  area  of  this  airway  is  a  =  7  X  7  =  49  sq.  ft. 
Substituting  this  and  the  given  value,  v  =  300  in  the  formula  given  in 
Art.  16  for  finding  the  quantity  of  air, 

0  =  az,  =  49X300=  14,700  cu.  ft.  per  min.     Ans. 

Ill 


2  MINE   VENTILATION  §13 

(12)  (a)  The  term  mine  resistance  means  the  resistance  offered  by 
the  airways  of  a  mine  to  the  passage  of  an  air-current.     See  Art.  17. 

(£)     See  Art.  17. 

(13)  (a)  The  term  coefficient  of  friction  is  used  to  describe  the 
unit  of  mine  resistance,  assuming  this  to  be  equal  to  the  resistance,  in 
pounds,  offered  by  1  sq.  ft.  of  the  rubbing  surface  of  the  airway  to  an 
air-current  having  a  velocity  of  1  ft.  per  min.     See  Art.  18. 

(*)     See  Art.  19. 

(14)  The  perimeter  of  this  airway  is  o  =  2(7  +  8)  =  30  ft.;  the  rub- 
bing surface  is  5  =  lo  =  3,000  X  30  =  90,000  sq.  ft.     Substituting  this 
and  the  given  value  for  the  velocity  of  the  air-current  v  =  500,  in  the 
formula  given  in  Art.  2O  for  finding  the  resistance, 

^  =  k  s  v"  -  .00000002  X  90,000  X  500"  =  450  Ib.     Ans. 

(15)  In  this  formula,  p  stands  for  the  unit  ventilating  pressure, 
k  for  the  coefficient  of  friction,  s  for  the  rubbing  surface  of  the  airway, 
v  for  the  velocity  of  the  air-current  and  a  for  the  sectional  area  of  the 
airway.     The  total  pressure  p  a  exerted  on  the  sectional  area  of  an 
airway  overcomes  the  resistance  k  s  v*  offered  by  the  airway  to  the 
passage  of  the  air-current,  and  is  therefore  equal  to  the  resistance. 
See  Art.  2O.     The  unit  of  ventilating  pressure  p  or  the  pressure  per 
square  foot  is  therefore  equal  to  the  resistance  divided  by  the  sectional 


area  -of    the   airway,   as  expressed    by  the    formula  p  =  —-.     For 

example,  the  resistance  offered  by  the  airway  in  question  14  was  found 
to  be  450  Ib.;  the  area  of  the  airway  is  a  =  7  X  8  =  56  sq.  ft.  The 
unit  of  ventilating  pressure  in  this  case  is  then 


=  8.04  Ib.  per  sq.  ft.     Ans.     See  Art.  22. 


(16)  (a)  See  Art.  23. 
(*)  See  Art.  26. 

(17)  The  work  performed  each  minute  in  producing  this  velocity 
in  this  airway  is  found  by  Substituting  values  in  formula  2  of  Art.  24. 
The  rubbing  surface  of  this  airway  was  found  in  question  14  to  be 
s  =  90,000  sq.  ft.     Then, 

u  =  ksv3  =  .00000002  X  90,000  X  5003  =  225,000  ft.-lb.  per  min. 
The  horsepower  producing  the  circulation  is  then  found  by  substi- 
tuting this  value  for  the  work,  u  =  225,000  in  the  formula  in  Art.  26, 

225,000 
h  =  '  = 


(18)  (a)  See  Art.  28. 
(b)  See  Art.  31. 

(19)  (a)  and  (£)  See  Art.  33. 


§13  MINE   VENTILATION  3 

(20)  Since   each  inch    of  water-column    represents  a  pressure  of 
5.2  Ib.  per  sq.  ft.,  as  explained  in  Art.  33,  the  pressure  per  square 
foot  in  this  airway  is/  =  5.2  X  1.5  =  7.8  Ib.     The  area  of  the  airway 
is  a  =  6  X  7  =  42  sq.  ft.     The  total  ventilating  pressure  in  this  case 
is,  therefore,  Art.  12, 

p  =  p  a  =  7.8  X  42  =  327.6  Ib.     Ans. 

(21)  The  rubbing  surface  of  this  airway  was  found  in  question  14 
to  be  s  =  90,000  sq.  ft.     Its  area  is  7  X  8  =  56  sq.  ft.     Substituting 
these  values  in  formula  2  of  Art.  38, 

_  .00000002  X  90,000  X  q*  _  .0018?' 
56s  ™  175,616 

175,616  X  10  =  .0018  g';  or,  .0018?'  =  -175,616  X  10 


.  975,644,444+ 


q  =  V975.644.444  =  31,235  cu.  ft.  per  min.     Ans. 

(22)  This  is  the  same  airway  as  that  given  in  question  14,  and  its 
rubbing  surface  is  s  =  90,000  sq.  ft.  Since  1  H.  P.  is  33,000  ft.-lb., 
Art.  26,  the  power  producing  the  circulation  in  this  case  is 
u  =  33,000  X  15  =  495,000  ft.-lb.  per  min.  Substituting  these  values 
in  formula  2  of  Art.  24, 

495,000  =  .00000002  X  90,000  X  v3  =  .0018  v3 
.0018  v3  =  495,000 


,000,000  =  650+  ft.  per  min.    Ans. 

(23)     Substituting  the  given  values  in  formula  2  of  Art.  42,  the 
area  of  the  opening  in  the  regulator  is 


a  =  .00038  =  9.2  sq.  ft.     Ans. 

VT75 

(24)  No;    two  ventilators  of  equal  power  operating  at  the  same 
time  on  a  single  airway  will  not  produce  double  the  quantity  of  air 
that  one  of  these  ventilators  will  produce  working  alone  on  the  same 
airway,   because  the  resistance  due  to  the  increased  velocity  of   air 
increases   more   rapidly  than  the  power,  and  to  double  the  quantity 
of  air  in  circulation  will  require  23  =  8  times  the  power,  as  explained 
in  Art.  43.     In  this  case  the  power  being  double,  the  quantity  will 
be  increased  in  the  ratio  of  ^(2  =  1.26,   nearly.     That    is  to  say,    if 
each  ventilator  when  working  alone  will  circulate  10,000  cu.  ft.  of  air 
per  min.  in  the  given  airway,  together  they  will  circulate  12,600  cu.  ft. 
per  min.  in  that  airway. 

(25)  Other  things  being  equal,  the  pressure  producing  a  circula- 
tion is  proportional  to  the  length  of  the  airways,  or  the  pressure  ratio 


4  MINE   VENTILATION  §13 

of  the  two  airways  is  equal  to  their  length  ratio,  as  shown  by  formula  1 
of  Art.  51.  Hence,  to  maintain  the  same  velocity  of  the  air  in  an 
airway  when  its  length  has  been  doubled  the  pressure  must  be 
doubled  likewise. 

(26)  Other  things  being  equal,  the  pressure  producing  a  circula- 
tion is  proportional  to  the  square  of  the  quantity  of  air,  or  the  pres- 
sure ratio  is  equal  to  the  square  of  the  quantity  ratio,  as  shown  by 
formula  3  of  Art.   51.     Hence,  to  double  the  quantity  of  air  in  a 
mine  or  airway  will  require  2'  =  4  times  the  original  pressure. 

(27)  Other  things  being  equal,  the  power  producing  a  circulation 
is  proportional  to  the  cube  of  the  quantity  of  air,  or  the  power  ratio 
is  equal  to  the  cube  of  the  quantity  ratio.     See  Art.  48.     Hence,  to 
double  the  quantity  of  air  in  a  mine  or  airway  will  require  23  =  8  times 
the  power.     See  also  Art.  43. 

(28)  For  the  purposes  of  ventilation  only,  that  airway  is  best  that 
will  pass  the  largest  quantity  of   air  with  .the  least  expenditure  of 
power;  that  is  to  say,  the  ratio  of  the  quantity  of  air  in  circulation  to 
the  cube  root  of  the  power  producing  the  circulation  should  be  a 
maximum,  as  explained  in  Art.  52.     This  ratio  is  expressed  by  trans- 
posing formula  1  in  Art.  38  to  read  *—  =  — .     Extracting  the  cube 
root  of  both  members  of  this  equation,  and  substituting  for  s  its  value 

s  =  lo,  then  -~  =  — - — .     The  airway,  therefore,  that  will  give  the 
\tt        ^k  lo 

greatest  value  for  the  expression  — =  =,  or  in  this  case,  since  k  and  I 

\klo 
are  both  constant,  the  airway  that  will  give  the  greatest  value  for 

-^  will  prove  the  best  airway  for  the  purposes  of  ventilation.     The 

perimeters  and  areas  and  the  values  of  this  expression  for  each  airway 
are  as  follows: 
First  airway: 

o  =  2(8  +  8)  =  32  ft.;  a  =  8  X  8  =  64  sq.  ft.;  ^=  =  —  =  20.15; 

\0        \32 

Second  airway: 

o  =  2(6  +  10)  =  32  ft.;  a  =  6  X  10  =  60  sq.  ft.;  4=  =  -?L  =  18.90; 

tjo        3132 

Third  airway: 
o  =  2(5  +  10)  =  30  ft.;  a  =  5  X  10  =  50  sq.  ft.;  -|=  =  — =  =  16.09. 

These  numbers  represent  the  relative  quantities  that  the  same  power 
will  circulate  in  each  of  these  airways.  Thus,  the  power  that  will 
circulate  20,150  cu.  ft.  of  air  per  min.  in  the  first  airway  will  circulate 


§13  MINE   VENTILATION  5 

18,900  cu.  ft.  per  min.  in  the  second  airway  and  16,090  cu.  ft.  per  min. 
in  the  third  airway. 

(29)     In  this  case,  comparing  the  two  airways,  the  quantity  ratio  is 
—  =  ^-QJQ  =  7>  and  calling  the  side  of  the  second  airway  x,  that  of 

the  first  airway  being  V64  =  8,  the  ratio  of  the  sides  is  -/-  =  %.     The 

at         8 

length  of  the  airways  and  the  power  being  the  same  in  each  case  their 
ratios  will  each  be  1.  Hence,  substituting  these  values  in  the  formula 
for  the  general  power  ratio  in  Art.  54, 

*  1  —  l  v  i  —  i    v  i -i 

—  \  8  /          \4/ 

/4 
Multiplying  both  sides  of  this  equation  by  (^ 

The  last  term  reduces  to  1  which  gives 

/4\3_M'orM'_/4\3_64 
W          W          W          W         27 
Extracting  the  fifth  root  of  both  sides  of  this  equation, 


*         »  ot 

8  =   \27  =  L188+ 
x  —  8  X  1.188  =  9.5+  ft. 
Since  the  airway  is  square,  its  area  is  then 

a  =  x*  =  9.52  =  90.25  sq.  ft.     Ans. 


MINE  VENTILATION 

(PART  2) 


(1)  The  division  of  the  air-current  passing  through  a  mine  or  air- 
way into  two  or  more  currents  is  called  splitting  the  air.     By  this 
means,  a  larger  quantity  of  air  is  circulated  by  the  same  power  in  the 
same  mine,  or  a  smaller  power  is  required  to  circulate  the  same  quan- 
tity of  air  in  the  same  mine.     See  Arts.  1  and  5. 

(2)  Splitting  the  air  always  causes  a  fall  of  pressure.     See  Art.  2. 

(3)  Because  the  splitting  of  the  air  reduces  the  ventilating  pressure 
and  permits  a  larger  quantity  of  air  to  flow  into  and  through  the  mine. 
The  increase  of  the  quantity  of  air  passing  through  the  main  intake 
airway  up  to  the  point  where  the  split  is  made  causes  an  increased 
consumption  of  power  in  this  main  airway,  and  therefore  reduces  the 
power  on  the  air  at  the  point  of  split.     See  Art.  2. 

(4)  When  the  resulting  velocity  of  the  air-current  is  too  low  to 
sweep  away  the  accumulating  gases.     See  Art.  4. 

(5)  See  Art.  5. 

(6)  The  natural  division  of  an  air-current  is  such  a  division  of  the 
air  as  results  when  all  the  airways  are  left  open  to  the  free  passage  of 
the  current,  the  airways  being  unobstructed  by  any  regulator  or  other 
device  for  increasing  the  resistance  of  the  airway  and  thus  reducing 
the  flow  of  air  through  the  same.     See  Art.  8. 

(7)  The  perimeters  and  areas  of  these  airways  are  as  follows: 

A,  o  =  2(6  +    8)  =  28  ft.;  a  =  6  X    8  =  48  sq.  ft. 

B,  o  =  2(8  +  12)  =  40  ft.;  a  =  8  X  12  =  96  sq.  ft. 

C,  o  =  2(6  +  10)  =  32  ft.;  a  =  6  X  10  =  60  sq.  ft. 
The  relative  potential  for  the  airways  is  then  as  follows: 

mr  -     I    **  AI\    .     I 

fl  » 

B, 
C, 


2  MINE  VENTILATION  §14 

Then,  canceling  those  factors  that  are  common  to  all  these  expres- 
sions and  reducing, 

~4~ 


.4  =  1.976 


I  X  =  X,  +  X,  +  X3  =  8.245 
Finally,  for  the  quantity  of  air  passing  in  each  respective  airway, 

O    100 

A,  q,  =  25,000  X  |^|  =    6,483  cu.  ft. 


25,000  X  =  12,526  cu.  ft. 


C,  qa  =  25,000  X  ^~  =    5,991  cu.  ft. 

Total  quantity,     25,000  cu.  ft. 

(8)  The    quantity   of    air    passing    in    each    split    is    160,000  -r-  4 
=  40,000  cu.  ft.  per  min.     The  perimeter  and  area  of  the  airways  are 
o  =  2  (8  +  10)  =  36  ft.,  and  a  =  8  X  10  =  80  sq.  ft.     Substituting  these 
values  in  the  formula  for  finding  the  horsepower,  the  power  consumed 
in  each  split  is  (see  Art.  11), 

,          kloq3          .00000002  X  3,000  X  36  X  40.0003 

h  =  WWa*=  33,000  X  80*  =  8.182  H.  P. 

The    total  power  consumed  in    the    four   splits    is    then   4  X  8.182 
=  32.728  H.  P. 

(9)  The    quantity   of    air   passing    in    each    split    is   50,000   -r-    2 
=  25,000  cu.  ft.  per  min.     The  perimeter  and  area  of  the  airways  are 
o  =  2(6  +  8)  =  28  ft.,  and  a  =  6  X  8  =  48  sq.  ft.     Substituting  these 
values  in  the  formula  for  finding  the'  unit  of  ventilating  pressure, 

_  kloq*  _  .00000002  X  6,000  X  28  X  25,000" 

'  ~      a3  ~  48s 

sq.  Ic.     Ans. 

(10)  (a)  The  first  step  is  to  calculate  the  natural  division  of  the 
air  (see  Art.  12).     The  perimeters  and  areas  of  these  airways  are  as 
follows: 

A,  o  =  2(8  +  10)  =  36  ft.;  a  =  8  X  10  =  80  sq.  ft. 

Bt  o  =  2(6  +  12)  =  36  ft.;  a  =  6  X  12  =  72  sq.  ft. 

C,  o  =  2(8  +    8)  =  32  ft.;  a  =  8  X    8  =  64  sq.  ft. 

Then  for  the  three  airways, 

A, 


§14  MINE  VENTILATION 

B,  X, 


/2.000  X  32 
Canceling  the  factors  common  to  all  these  expressions  and  reducing, 

A  Xi  =  10 A/    -     =  10 .  /10 

I     o 

B, 

'c, 

V  &    /\    <J  Kirf 

16.243 

The    quantity  of   air  passing   in  each  respective   split  is  then  as 
follows: 


A,  9l  =  150,000  X  jgHj  =   56,203  cu.  ft. 

B,  g,  =  150,000  X  ^^  =  41,556  cu.  ft. 

C,  g,  =  150,000  X  =   52,241  cu.  ft. 


Total  quantity,      150,000  cu.  ft. 

The  unit  of  ventilating  pressure  calculated  for  any  one  of  these  splits 
will  be  the  pressure  causing  the  circulation,  since  the  pressure  is 
assumed  to  be  the  same  at  the  mouth  of  all  the  splits.  Hence,  sub- 
stituting the  values  for  split  A  in  the  formula  for  finding  the  unit  of 
ventilating  pressure, 

kloq*        .00000002X3,000X36X56,203'        1Q  ___  ,. 
p  =  —  —  *-  =  —  —  g^  —  —  =  13.326  Ib.  per  sq.  ft. 

Ans. 

(6)  The  horsepower  producing  the  circulation  in  all  the  splits  is 
found  by  multiplying  the  unit  of  ventilating  pressure  at  the  point  where 
the  air  is  divided  by  the  total  quantity  of  air  in  circulation  and  dividing 
this  result  by  33,000;  thus, 

QP     _  150,000  X  13.326  _ 
H  =  33^000  ~  33,000  TO'57  H'  R     AnS' 

(11)     (a)  Applying  the  method  illustrated  in  the  answer  to  question  10 

-  -69714 


=   -63960 


^  X  =  X,  +  X,  +  X,  =  1.77868 


MINE  VENTILATION 


§14 


.69714 
1.77868 
.63960 


X  50,000  =  19,597  cu.  ft.  per  min.  for  1st  split. 


=  T^C^H  X  50,000  =  17,980  cu.  ft.  per  min.  for  2d  split, 

J. .  /  /  ouo 


44104 
gt  =  r^^  X  50,000  =  12,423  cu.  ft.  per  min.  for  3d  split. 


Ans. 


50,000 
(b)     Applying  the  formula  for  the  unit  ventilating  pressure, 

k  s  q*       .00000002  X  400,000  X  50,000' 
P  =  —r  '  —      *  —  =  per  sq>  ft' 


Therefore,  *  -  - 


=  30.3  H.  P.     Ans. 


(')    A  = 
Therefore,  h  =  ^ 


.00000002  X  96.000  X  19,597' 
—     — 


=  15.8  Ib.  per  sq.  ft. 


15.8  X  50,000 
~~~~ 


33,000 


(12)  (a)  The  first  step  is  to  calculate  the  perimeters  and  areas  of 
the  several  splits,  airways,  and  shaft  in  this  mine.  The  perimeters 
and  areas  are  as  follows: 

Haulage  slope,  o  =  2(  6  +  12)  =  36  ft.;  a  =    6  X  12  =    72  sq.  ft. 

Main  airway,    o  =  2(10  +  12)  =  44  ft.;  a  =  10  X  12  =  120  sq.  ft. 

Split  A,  o  =  2(  8  +  12)  =  40  ft.;  a  =    8  X  12  =    96  sq.  ft. 

Split  B,  o  =  2(  8  +  10)  =  36  ft.;  a  =    8  X  10  =    80  sq.  ft. 

Upcast  shaft,    o  =  2(10  +  10)  =  40  ft.;  a  =  10  X  10  =  100  sq.  ft. 

The  relative  pressure  potentials  in  this  case  will  be 

Haulage  slope,  X,  =  a\lf-  =    ~-  '        72 


Main  airway,     X, 
Split  A,  X, 

Split  B,  X< 


2.277 


=  7.071 


Upcast  shaft,     Xt  = 

The  sum  of  the  relative  potentials  for  the  two  splits  is  2  Xf  =  Xa  +  Xt 
=  3.806.  To  find  the  pressure  producing  the  circulation  in  the  mine, 
substitute  the  given  values  in  the  general  equation  for  finding  the  pres- 
sure producing  the  circulation,  Art.  14;  thus, 

p  =  .00000002  X  100,000'  (2^5  +  jfijyi  +  g-jjogi  +  ^oTp) 

=  64  Ib.  per  sq.  ft.     Ans. 

(b)  The  horsepower  producing  the  circulation  in  this  mine  is  found 
by  multiplying  the  unit  of  ventilating  pressure  obtained  in  (a)  by  the 


§14  MINE  VENTILATION  5 

total  quantity  of  air  passing  in  the   main  airway  and    dividing   by 
33,000;  thus, 

h  =  100,000  X  33^00  =  193.9,  say  194  H.  P.     Ans. 

(13)  See  Art.  15. 

(14)  It  is  important  that  the  ventilation  be  so  arranged  wherever 
practicable  that  the  air-current  will  tend  to  rise  as  it  passes  through 
the  workings.     See  Art.  21. 

(15)  An  air  column  in  ventilation  is  a  column  of  air  having  a  base 
of  one  square  unit,  which  is  usually  taken  as  1  sq.  ft.,  and  a  height 
equ.al  to  the  height  of  the  air  considered.     See  Art.  25. 

(16)  See  Art.  27. 

(17)  The  motive  column,  in  terms  of  the  downcast  air,  is  obtained 
by  substituting  the  given  values  in  formula  1  of  Art.  27.     Thus, 


The  pressure  corresponding  to  this  motive  column  is  found  by 
multiplying  the  height  of  the  column  by  the  weight  of  1  cu.  ft.  of 
downcast  air.  The  weight  of  1  cu.  ft.  of  this  air  having  a  tem- 
perature of  40  F°.,  assuming  a,  barometric  reading  of  30  in.  is 

'          '  ^r-  =  .079638  Ib.     The  pressure  due  to  the  motive  column 

~ 


is,  therefore,  p  =  Mw  =  243  X  .079638  =  19.352  Ib.  per  sq.  ft.     The 
water  gauge  corresponding  to  this  pressure  is  then 
.  _   P_  _  19.352 
~  5.2  "     5.2     : 

(18)  In  general,  rise  workings  are  the  most  difficult  to  ventilate 
because   the   current   returning  from    the  working  face  is  generally 
warmer  than  that  approaching  the  working  face.     The  warmer  air 
being  lighter  tends  to  rise,  and  the  colder  and  heavier  air  to  fall,  which 
assists  the  ventilation  of  dip  workings,  but  opposes  the  ventilation  of 
rise  workings.     See  Art.  33. 

(19)  See  Art.  42. 

(20)  For  the  same  conditions  with  respect  to  the  temperature  of 
the  shaft  and  the  circulation  of  air  through  the  mine  workings,  the 
quantity  ratio  varies  as  the  square  root  of  the  ratio  of  the  depths  of 
the  shaft  before  and  after  the  erection  of  the  stack.     See  Art.  45. 
The  shaft  being  200  ft.  deep  and  the  stack  40  ft.  high,  the  ratio  of  the 

240 

depth  after  the  erection  of  the  stack  to  that  of  the  shaft  is  ^r~.  Call- 
ing the  increased  quantity  of  air  in  circulation  x  the  quantity  ratio  is 
x  ,  x  /240  _ 

1C6>  60^00  "  \206  ~ 
60,000  X  VL2  =  60,000  X  1.095  =  65,700  cu.  ft.  per  min.     Ails. 


MINE  VENTILATION 

(PART  3) 


(1)  (a)   Disk  or  propeller  fans  and  centrifugal  fans.     See  Art.  6. 
(d)     Open  running  fans  and  closed  running  fans.     See  Art.  8. 

(2)  It  is  necessary  to  give  the  outer  and  the  inner  diameters  and 
the  width  of  the  fan;  also,  the  number,  shape,  and  position  of  the  fan 
blades.     See  Art.  8. 

(3)  See  Art.  9. 

(4)  In  the  case  of  an  exhaust  fan,  the  intake  opening  of  the  fan  is 
connected  with  the  return  airway  of  the  mine  and  the  mine  air  is  thus 
drawn  into  the  fan,  from  which  it  is  discharged  into  the  atmosphere. 
In  the  case  of  the  blower  fan,  the  discharge  opening  of  the  fan  is  con- 
nected with  the  intake  airway  of  the  mine  while  the  intake  orifice  is 
open  to  the  atmosphere.     Air  is  thus  drawn  into  the  fan  from  the 
atmosphere  and  discharged  into  the  mine.     The  direction  of  the  air 
through  the  fan  is  the  same  in  each  case.     See  Art.  9. 

(5)  (a)  The  fan  housing  encloses  the  fan  wheel  and  conducts  the 
air  from  the  mine  to  the  fan  when  exhausting,  or  from  the  fan  to  the 
mine  when  blowing.     See  Art.  11. 

(b)  The  expansion  of  the  fan  casing  should  begin  at  a  point  on  the 
circumference  of  the  fan  wheel  at  a  distance  from  the  point  of  cut-off 
at  least  equal  to  the  distance  between  two  consecutive  blade  tips. 
From  this  point,  the  casing  should  expand  uniformly  so  that  the  sec- 
tional area  of  the  spiral  passage  encircling  the  fan  will  be  uniform, 
and  the  velocity  of  the  air  will  then  be  uniform  all  around  the  fan. 
See  Art.  11. 

(6)  See  Art.  12. 

(7)  The  chief  causes  of  vibration  in  a  fan  are  lack  of  proportion- 
ment  between  the  different  parts  of  the  fan,  or  the  striking  of  the  air- 
current  against  abrupt  angles  or  surfaces,  causing  eddies  to  be  set  up  in 
the  air-current.     Vibration  is  often  caused  by  the  rapid  succession  of 

2  15 


2  MINE  VENTILATION  §15 

blows  imparted  to  the  air  by  the  blades  of  the  fan  passing  the  edge  of 
a  straight  cut-off.  The  several  means  taken  to  prevent  this  trouble 
are  a  careful  proportionment  of  the  different  parts  of  the  fan  to  the 
work  to  be  performed;  avoiding  sharp  angles  and  abrupt  changes  in 
the  sectional  area  of  the  airways;  also  using  a  V-shaped  cut-off  or 
shutters  in  the  fan.  See  Art.  14. 

(8)  See  Art.  17. 

(9)  The  Nasmyth  fan  is  an  open-running  fan;  it  has  straight  radial 
blades    supported  on  radial    arms  that   are    bolted  to  two    cast-iron 
spiders  mounted  on  the  fan  shaft,  to  which  they  are  firmly  keyed. 
See  Art.  2O. 

(10)  The  Guibal  fan  is  a  closed-running  fan;  its  blades  are  straight 
like  the  Nasmyth,  but  are  not  radial,  being  inclined  backwards  from 
the  direction  of  motion.      The  chief  feature  of  the  Guibal  fan  is  the 
frame  that  supports  the  blades;   this  consists  of  a  series  of  pairs  of 
double  bars,  one  end  of  each  bar  supports  a  blade,  while  the  other  end 
forms  a  brace  for  one  of  the  opposite  blades.     The  spiral  of  the  Guibal 
fan  extends  only  one-quarter,  and  in  more  recent  types  of  this  fan  one- 
half,   around  the  circumference,   the  remainder  of   the  circle  fitting 
closely  to  the  fan  wheel.      See  Art.  21. 

(11)  (a)  The  Waddle  fan  is  an  open-running  fan  having  tapered 
blades  that  are  curved  backwards  from  the  direction  of  rotation.     See 
Art.  22. 

(b)  The  Schiele  fan  is  a  closed-running  fan,  the  fan  wheel  being 
enclosed  in  a  spiral  casing.  In  most  other  respects,  it  resembles  the 
Waddle  fan  except  for  the  sheet-iron  diaphragm  that  divides  the  fan 
practically  into  two  single-inlet  fans.  See  Art.  23. 

(12)  (a)  Substituting   the    given   value    for   Q   in    formula    1    of 
Art.  28,  the  diameter  of  the  intake  opening  is 

d  =  .03257 A/150,000  =  12.6+  ft.,  or  say  12  ft.  6  in.     Ans. 
(b)     Substituting  the  same  value  in  formula  2  of  Art.  28,  the  diam- 
eter of  the  central  opening  for  a  double-intake  fan  is 

d  =  .023Vl50,000  =  8.9,  say  9  ft.     Ans. 

(13)  (a)  The  velocity  of  the  air  entering  the  fan.     This  is  assumed 
as  varying  from  1,000  to  1,500  ft.  per  min.,  the  average  velocity  for  the 
purpose  of  calculation  being  taken  as  1,200  ft.  per  min.     See  Art.  28. 

(b)  The  deflection  of  the  air  entering  the  fan,  or  the  change  in  its 
direction,  causes  a  loss  of  velocity  that  is  assumed  to  equal  about 
20  per  cent.,  thus  making  the  velocity  of  the  air  passing  through  the 
throat  of  the  fan  about  eight-tenths  of  its  velocity  at  the  intake  opening. 
On  account  of  this  loss  of  velocity,  the  area  of  the  throat  of  the  fan 


§15  MINE  VENTILATION  3 

must    be  increased    in    the  same  ratio  as  the  velocity  is  decreased. 
See  Art.  29. 

(14)  (a)  Substituting  the  given  values  in  the  formula  in  Art.  3O, 
the  volume  of  this  fan  is 

V  =  .7854  (16*  -  10')  4.5  =  551+  cu.  ft.     Ans. 
(t>)     The  weight  of  the  revolved  air  in  this  case  is 
W  =  .083  X  551  =  45.7+  Ib.     Ans. 

Now,  finding  the  distance  of  the  center  of  gravity  of  the  air  in  one 
compartment  of  this  fan  by  substituting  the  given  values  in  formula  2 
of  Art.  31,  assuming  a  uniform  density  of  the  air  in  the  fan, 


The  circumference  of  the  circle  described  by  this  radius  is 

2  TT  Re  =  2  X  3.1416  X  6.6  =  41.47  ft. 

and  the  velocity  of  the  center  of  gravity  of  the  air  in  each  compart- 
ment of  the  fan  at  a  speed  of  100  rev.  per  min.  is 

*-«»*£«  =  69.1  ft.  per  sec. 

Substituting  these  values  in  formula  1  of  Art.  31,  the  centrifugal 
force  due  to  the  action  of  this  fan  is 
..,      45.7  X  69.  1* 


32.16X6.6 

(c)  Substituting  the  values  thus  found  and  the  given  values  in 
formula  2  of  Art.  32,,  the  acceleration  due  to  the  fan's  action  at  the 
given  speed  is 

f  =  '6°  ^J>'—  X  32.16  =  24.795,  Say  24.8  ft.  per  sec.    Ans. 
o(JU 

Finally,  assuming  the  sectional  area  in  the  fan  drift  where  the 
quantity  and  pressure  are  measured  is  a  =  120  sq.  ft.;  the  unit  of 
ventilating  pressure  corresponding  to  the  given  mine  resistance  is 

800 
p  =  ^20  =  6.67  Ib.  per  sq.  ft.     Substituting  this  and  the  other  values 

found  and  given  in  the  formula  for  finding  the  quantity  of  air  delivered 
by  the  fan  in  Art.  33, 

Q  =  60   ^  X  =  68,800  cu.  ft.  per  min.     Ans. 


NOTE.— This  fan  is  an  example  of  a  poorly  designed  fan,  as  will  be  shown  by  the 
following  example: 

(15)     (a)  For  a  double-intake  fan,  the  diameter  of  the  intake  open- 
ing and  the  width  of  the  fan  are,  respectively, 

d  =  .023>/1907)00  =  10.02,  say  10  ft.     Ans. 
A  =  -rf  =  3XlO  =  6.25  ft.,  or  6  ft.  3  in.     Ans. 

O  O 

First  find  the  value  of  X  =  <$$-  =  V^SW—  =  2,215+. 

145—34 


4  MINE  VENTILATION  §15 

Assuming  the  value  of  the  fan  constant  in  this  case  to  be  c  —  4,  and 
substituting  this  and  the  given  values  in  the  formula  given  in  Art.  35 
for  finding  the  ratio  of  the  outer  diameter  to  the  inner  diameter  of  the  fan, 


The  outer  diameter  of  the  fan  is  then 

D  =  md  =  1.6  X  10  =  16  ft.     Ans. 

NOTE.—  It  will  be  observed  that  this  fan  is  the  same  size  as  that  in  question  14, 
except  for  its  creator  width;  the  fan  in  question  14  is  4.5  feet  wide,  while  this  fan  is 
6.25  feet  wide. 

(b)  For  a  double-intake  fan,  the  diameter  of  the  intake  opening 
and  the  width  of  the  fan  are,  respectively, 

d  =  .023  V68,  800  =  6.033,  say  6  ft.     Ans. 
b  =  ~d  =  |  X  6  =  3.75,  or  3  ft.  9  in.     Ans. 

O  O 


The   value   of  X  in   this   case   is  X  =  \-  =  \p~  =  892+. 

\  f>          \    b.b/ 

Then,  taking  c  =  4,  and  substituting  this  and  the  given  values  in  the 
formula  in  Art.  35  for  rinding  the  ratio  of  the  outer  diameter  to  the 
inner  diameter  of  the  fan, 


,/Vl 

~  \ 


^p^r4+(™,  t+1.SJK 


The  outer  diameter  of  the  fan  is  then 

D  =  m  d  =  2.356  X  6  =  14.13  ft.,  or  say  14  ft.  2  in.     Ans. 

NOTE.—  This  fan  is  about  2  ft.  less  in  diameter  and  9  in.  narrower,  but  is  calcu- 
lated to  do  the  same  work  at  the  same  speed  as  that  in  question  14,  which  is  thus 
seen  to  be  too  narrow  with  respect  to  its  other  dimensions. 

(16)  Substituting  the  given  values  in  the  formula  for  finding  the 
fcorsepower  in  Art.  34, 


H  =  -—  =  SMOO  X  6.67 
33,000  K        33,000  X.  60 

(17)  The  fan  in  question  15  (a)  is  circulating  190,000  cu.  ft.  of  air 
per  min.  against  a  pressure  of  3.32  Ib.  per  sq.  ft.  Except  for  its  being 
wider,  it  has  the  same  dimensions  and  is  driven  at  the  same  speed  as 
the  fan  in  question  14.  Assuming  the  efficiency  of  the  fan  to  be 
60  per  cent,  as  stated,  the  horsepower  required  is 


The  fan  in  question  15  (d)  is  doing  the  same  work  as  that  in  ques- 
tion 14.  Though  a  smaller  fan,  a  test  would  probably  show  its 
efficiency  to  be  higher  on  account  of  its  being  better  proportioned. 
The  power  required  to  drive  the  fan  would  be  the  same  as  that  found 
in  question  16  unless  this  power  was  decreased  by  a  higher  efficiency 
of  the  fan. 


§15  MINE  VENTILATION  5 

(18)     Substituting  the  given  values  in  the  formula  for  finding  the 
static  pressure  or  water  gauge  due  to  a  fan  in  Art.  45, 

X  2.4  =  5.14+  h, 


(19)  (a)  See  Art.  46. 

(6)  Because  it  is  usually  impossible  or  impracticable  to  separately 

test  the  fan  and  the  motor  driving  the  fan. 

(20)  (a)  and  (£)  See  Art.  47. 


FUELS 


(1)  (a)  An  analysis  in  which  the  composition  of  a  fuel  is  expressed 
in  terms  of  moisture,  volatile  matter,  fixed  carbon,  ash,  and  usually, 
in  addition,  sulphur  and  sometimes  phosphorus,  as  determined  by  ulti- 
mate analysis. 

(£)     An  analysis  in  which  the  elementary  composition  of  a  fuel  is 
determined. 

(2)  Substituting  in  the  formula,  h  =  //"——,  given  in  Art.  4,  we 

o 

have  h  =  2.58  -  ^p  =  1-49  per  cent.     Ans. 

(3)  The  combustible  matter  in  the  coal  is  the  fixed  carbon  plus  the 
volatile  matter,  and  is  equal  to  57.3  +  36.3  =  93.6  per  cent,  of  the  coal; 
hence,  the  combustible  analyzes, 

Fixed  carbon,  -~  =  61.2  per  cent. 

qc  q 

Volatile  matter,  ~  =  38.8  per  cent.     Ans. 
.you 

(4)  A  good  steaming  coal  should  kindle  readily  and  burn  quickly 
but  steadily.     It  should  contain  only  enough  volatile  matter  to  insure 
rapid    combustion,   and  be  low   in   ash  and  sulphur.     It  should  not 
clinker  and   should  not  be  so  friable  as  to  be  too  badly  broken  in 
handling. 

(5)  Because  all  coals  cannot  be  burned  with  equal  efficiency  under 
all  conditions. 

(6)  An  actual  test  of  the  coals  should  be  made  in  the  furnace  to  be 
used,  under  the  ordinary  working  conditions  of  the  plant,  and  the  coal 
selected  that  is  best  suited  to  the  conditions.     A  proximate  analysis  of 
the  coal  selected  will  furnish  a  good  guide  for  the  selection  of  a  coal 
for  this  particular  plant. 

(7)  They  are,  the  cost  of  the  coal  in  the  ground,  or  royalty  to  th.e 
owner;  cost  of   mining  and    preparation  at  mine,   including  cost  of 
repairs,  interest  on  investment;  freight  rates;  cost  of  handling,  storing, 
selling,  insurance,  distribution  to  customers,  and  agents'  and  retailers' 

111 


2  FUELS  §  16 

profits;  relative  supply  and  demand  and  prejudice  in  favor  of  certain 
coals. 

(8)  (a)     The  generally  accepted  explanation  is  that  there  is  an 
absorption  of  oxygen  by  the  combustible  matter,  including  the  sulphur, 
producing  a  slow  combustion  that  generates  heat.     If  the  heat  thus 
produced  cannot  readily  escape,  the  temperature  may  rise  high  enough 
to  cause  ignition  or  active  combustion. 

(b)  It  occurs  most  often  on  shipboard,  where  the  coal  is  stored  in 
warm  and  poorly  ventilated  bunkers,  and  in  large  stock  piles.  Very 
fine  coal  absorbs  oxygen  more  readily  than  coarse,  hence  such  coal  is 
more  liable  to  spontaneous  combustion.  Freshly  mined  coal  absorbs 
oxygen  more  readily  than  coal  that  has  been  mined  for  some  time,  and 
hence  is  more  liable  to  spontaneous  ignition. 

(9)  The  powdered  coal  is  introduced  into  the  combustion  chamber 
of  the  furnace  by  means  of  a  blast  of  air,  the  lining  of  the  combustion 
chamber  being  first  heated  to  a  high  temperature  by  means  of  an  open 
fire.     The  distributing  nozzle  is  so  located  that  the  dust  is  distributed 
throughout  the  entire  space  of  the  combustion  chamber,  where  it  is 
rapidly  and  completely  burned. 

(10)  Its  advantages  are  that  it  has  a  greater  heating  capacity  than 
coal;  is  easily  transported  in  pipes,  tank  cars,  or  tank  vessels;  the  cost 
of  handling  is  less  than  for  coal;  it  may  be  burned  without  smoke  and 
there  are  no  ashes  to  be  handled. 

Its  disadvantages  are  that  its  supply  is  limited,  and  in  most  localities 
its  price  is  high  as  compared  with  that  of  coal. 

(11)  It  is  introduced  into  the  firebox  or  combustion  chamber  by  the 
use  of  burners  so  constructed  that  the  oil  is  mixed  with  a  jet  of  steam 
or  compressed  air  and  thus  converted  into  a  fine  spray  as  it  enters  the 
combustion  chamber. 

(12)  Natural  gas,  coal  gas,  water  gas,    producer  gas,  combined 
water  gas  and  producer  gas,  blast-furnace  gas  and  coke-oven  gas. 

(13)  The  carbon  is  completely  burned  to  carbon  dioxide  and  the 
hydrogen  to  water.     With  methane,  Cfft,  the  reaction  is 

CHt  +  2O,  =  CO,  +  2H,O 

(14)  In  burning  1  Ib.  of  carbon  to  carbon  dioxide,  2f  Ib.  of  oxygen 
is  required  (Table  XXV).     In  burning  1  Ib.  of  hydrogen  to  water,  8  Ib. 
of  oxygen  is  required.     In  burning  1  Ib.  of  sulphur  to  sulphur  dioxide, 
I  Ib.  of  oxygen  is  required. 

The  amount  of  carbon  to  be  burned  is  .914  Ib.,  requiring  .914  X  2f 
=  2.437  Ib.  of  oxygen. 

Oft 

The  amount  of  available  hydrogen  is  2.59  —  -^  =  2.58  per  cent. 

o 

=  .0258  Ib.,  requiring  .0258  X  8  =  .2064  Ib.  of  oxygen. 


§  16  FUELS  3 

The  amount  of  sulphur  burned  may  be  assumed  as  one-half  of  the 
whole,  or  .105  per  cent.  =  .00105  lb.,  requiring  .00105  Ib.  of  oxygen. 

As  there  are  no  other  combustibles,  the  weight  of  oxygen  theoretic- 
ally required  to  burn  the  coal  is: 

POUNDS 

For  the  carbon 2.43700 

For  the  hydrogen 20640 

,        For  the  sulphur 00105 

Total 2.64445 

Since  oxygen  makes  up  only  23  per  cent,  of  the  air  by  weight,  the 

2  644 
weight  of  air  theoretically  required  is  —93-  =  H-5  lb.    Ans. 

(15)  The  temperature  of  ignition  is  the  temperature  at  which  a 
given  body  takes  fire.     The  temperature  of  the  fire  is  the  temperature 
produced  by  the  burning  of  a  body. 

(16)  Applying  the  formula  in  Art.  133, 

_,      616  C+  2,220  H  -  327  O  -  44  W 

T  =  /+.02y+.18// ,  we  have 

„,  _  616  X  81.15  +  2,220  X  5.21  -  327  X  2.24  -  44  X  .69  _      0 

19.8+.02X  .69 +.18X5.21 
T+  t  =  2,929.5  +  75°  =  3,004.5°  F.  Ans. 

(17)  Applying  formula  in  Art.  136,  pounds  of  dry  air  per  pound 

3.032  N  3.032  X  80.2 

of  carbon  =  cc>a  +  c&  we  have     n  5  +  9      =  19-6  lb-  of  air  Per 

pound  of  carbon  burned.  Since  the  coal  contains  76  per  cent,  of  car- 
bon, there  are  2,000  X  .76  =  1,520  lb.  of  carbon  in  1  T.  of  coal.  The 
total  weight  of  air  required  will  then  be  1,520  X  19.6  =  29,792  lb.  Ans. 

(18)  Substituting  in  Dulong's  formula,  Art.   138,  heating  value 
=  Ioi)X  T14'600  C* 82,090 /AT-  ^\  + 4,000  sl,  we  have 
Heating  value  =  ~  [14,600  X  82.89  +  62,000  X  4.48  +  4,000  X  .68] 

=  ^  [1,210,194  +  277,760  +  2,720]  =  14,906.7  B.  T.  U.     Ans. 

•      (19)     The  value  of  K  for  a  Pocahontas  coal  is  given  in  Table  XXIX 
as  15,829.     Substituting  in  formula  1,  Art.  14O,  we  have 
15,829  (100  -  3.11  -  .68  -  1.5)  +  (.58  X  4,050)  =  15  030  ^3  T  u 

Ans. 

(20)     Substituting  in  the  formula  in  Art.  145,  we  have 
(9  X  .0521  +  .0069);x  [(212  -  70)+  965.8  +  .48  (580  -  212)]  =  .4758 
X  [142  +  965.8  +  176.64]  =  611.14  B.  T.  U.     Ans. 


4  FUELS  §  16 

(21)  Self-filling  buckets,  flight  conveyers,  belts,  continuous  lines 
of  metal  buckets,  chutes,  and  car-dumping  machines. 

(22)  The  reasons  for  storing  coal  are:  at  the  points  of  consumption, 
to  insure  no    interruption  in    supply  from  uncertain  transportation, 
strikes  and  other  causes;  at  the  mines,  to  permit  of  the  mines  being 
run  continuously  when  the  demand  for  coal  is  small;    and  in  cold 
climates;  to  take  advantage  of   the  cheaper  transportation  by  water 
during  a  portion  of  the  year. 


INDEX 


NOTE. — All  items  in  this  index  refer  first  to  the  section  and  then  to  the  p 
section.  Thus  "Advance  of  a  mine  explosion,  §6,  p27,"  means  that  advance 
explosion  will  be  found  on  page  27  of  section  6. 


of  the 
a  mine 


Absolute  pressure,  §5,  p31. 

temperature,  §5,  p!7. 

zero,  §5,  p!7. 
Adjustment  of  the  mercurial  barometer,  §5, 

P30. 

Advance  of  a  mine  explosion,  §6,  p27. 
Affinity,  §5,  pi. 
Afterdamp,  §6,  pll. 
Air  bridges,  §13,  p7. 

columns,  §14,  p38. 

columns,  Average  temperatures  of,  §14,p44. 

columns,  Density  of,  §14.  p49. 

courses,  §13,  p2. 

crossings,  §13,  p7. 

Density  of,  referred  to  hydrogen,  §5,  p52. 

Effect  of  splitting  the,  §14,    p2. 

Explosive  condition  of  mine,  §6,  p!5. 

Fuel  burned  in,  §16,  p72. 

in  mines,  Condition  of,  §6,  p!5. 

measurements,  §13,  p25. 

Power  on  the,  §13,  p24. 

Properties  of,  §16,  p74. 

Quantity  of,  delivered  by  fan,  §15,  p35. 

Quantity  of,  in  circulation,  §13,  p!7. 

Quantity   of,    produced   by   two   or   more 
ventilators,  §13,  p51. 

Required,  Quantity  and  velocity  of,  §14, 
P24. 

Relation    of    velocity    or    quantity    of,    to 
power,  §13,  p55. 

Relative  humidity  of,  §16,  p74. 

required  by  law,  Quantity  of,  §14,  p25. 

Shaft,  §13,  p2. 

Splits,  §14,  P8. 

supply,  Estimation  of,  §16,  p83. 

To  measure  the  velocity  of,  in  an  airway. 
§13,  p25. 

Weight  of  one  cubic  foot  of,  §5,  p5l. 

-current,  Calculation  of  work  of  producing 
an,  §13,  p23. 


Air — (Continued) 

-current,  Natural  division  of  the,  §14,  p9. 
-current,  Proportionate   division  of    the, 

§14,  P9. 

-current.  Reversing  the,  §15,  p!7. 
-current,  Velocity  of,  §13,  p!7. 
-currents,  Conducting,  §13,  pi. 
-currents,  How  air  columns  produce,  §14, 

P38. 

-currents,  How  produced,  §13,  p!3. 
-currents,  Production  and  control  of,  §13, 

Pi. 

-currents,  Splitting,  §14,  pi. 
Airway,  Calculation  of  the  resistance  of  an, 

§13,  p20. 

Perimeter  of,  §13,  p9. 
Relation  between  perimeter  of,  and  power, 

§13,  P54. 
Relation  between  the  length  of  an,  and  the 

power,  §13,  p54. 
Rubbing  surface  of,  §13,  pll. 
Sectional  area  of,  §13,  plO. 
To  measure  the  velocity  of  air  in  an,  §13. 

p25. 

Value  of,  §13,  p!8. 
Airways,  §13,  p2. 
Choice  of,  §13,  P65. 
Comparing  similar,  §13,  p67. 
Comparison  of  forms  of,  §13,  pll. 
Form  and  size  of,  §13,  p9. 
General  power  ratio  for  similar,  §13,  p67 
General  ratio  for  similar,  §13,  p67. 
Similar,  §13,  p!3. 
Single,  or  circulations,    §13,  p46. 
Analysis  of  coal  and  coke,  §16,  p91. 
Proximate,  §16,  pp4,  91. 
Report  of  coal,  §16,  p97. 
Selling  coal  bv,  §16,  p30. 
Ultimate,  §16,  pp4,  96. 
Valuing  coals  by,  §16.  p28. 
Anemometer,  Biram,  §13,  p26. 


IX 


INDEX 


Anemometer — (Continued) 

Self-timing,  §13,  p27. 

Special,  §13,  p27. 

Use  of  the,  §13,  p29. 
Aneroid  barometer,  The,  §5,  p32. 
Animal  oils,  §6,  p58. 
Approaching  a  body  of  gas,  §6,'  p63. 
Area  and  power,  Relation  between,  §13,  p55. 
Arrest  of  an  explosion,  §6  p28. 
Artificial  ventilation,  §13,  p!4. 
Ash,  §16,  P3. 

Determination  of,  in  coal  §16,  p93. 

in  coal,  §16,  p!8. 

Ashworth-Hepplewhite-Gray  lamps,  §6,  p47. 
Atmosphere,  Composition  of,  §5,  p51. 

Dangerous,  §  6,  pi 6. 

Extinctive  character  of  an,  §6,  p!8. 

Fatal,  §6,  p!6. 

The,  §5,  p51. 
Atmospheres,  §5,  p31. 

Table  of  composition  of  fatal,  §6,  p!7. 
Atmospheric  pressure;  §5,  p28. 

Measurement  of,  §5,  p29. 
Atomic  weight,  §5,  p38. 
Atoms,  §5,  pi. 

Automatic  railway,  Hunt,  §16,  p!03. 
Avogadro's  law,  §5,  p45. 

B 

Bagasse,  §16,  plO. 

Barometer,  Adjustment  of  the  mercurial,  §5, 
p30. 

The  aneroid,  §5,  p32. 

The  mercurial,  §5,  p30. 
Beard-Mackie  sight  indicator,  §6,  p68. 
Beaume's  hydrometer,  §5,  pll. 
Belt  conveyer,  Tripper  for,  §16,  p!07. 

conveyers,  §16,  p!06. 
Belts  for  conveyers,  §16,  p!06. 
Bench  of  retorts,  Operating,  §16,  p61. 
Biram  anemometer,  §13,  p26. 
Bituminous    coal,    To    prevent    spontaneous 

ignition  of,  §16,  p35. 
Blackdamp,  §6,  p3. 
Blacksmith  coals,  §16,  p!7. 
Blades  of  fan,  Number  of,  §15,  p38. 

of  fans,  Curvature  of.  §15,  p39. 

of  fans,  Inclination  of,  §15,  p40. 

of  fans,  Secondary,  §15,  p39. 

Tapered  fan,  §15,  p41. 
Blasting  powder,  Temperature  of  flame  of, 

§6,  p!3. 

Blower  fan,  §  15,  p7. 
Blowers  and  feeders,  §5,  p53. 
Blowing  system  of  ventilation,  §13,  p!5. 
Blow-down  fan,  §15,  p7. 
Bonneted  Clanny  Lamp,  §6,  p42. 


Bonneted — (Continued) 

Davy  lamp,  §6,  p39. 

Marsaut  lamp,  §6,  p47. 

Mueseler  lamp,  §6,  p45. 
Box  regulator,  §13,  p5. 
Brattices,  §13,  p6. 

Bridge  tramway  storage  system,  §16,  p!24 
Bridges,  Air,  §13,  p7. 
Briqueting  fuel,  Machines  for,  §16,  p39. 
Briquets,  §16,  p38. 
British  thermal  unit,  §5,  pig. 
Brown  car-dumping  machine,  §16,  pl!8. 
Bucket  carriers,  §16,  p!09. 

Clam-shell,  §16,  p98. 

conveyer,  §16,  pl!2. 

Drop-bottom,  §16,  plOO. 

elevators,  §16,  pllO. 

Orange-peel,  §16,  p99. 

Shovel,  §16,  plOO. 
Buckets,  Self-filling,  §16,  p98. 
Burner,  Coal-dust,  §16,  p37. 
Burners,  Flat-jet  petroleum,  §16,  p47. 

oil,  Injector,  §16,  p49. 
Burning  of  wood,  §16,  plO. 


Caking  and  non-caking  coal,  §16,  p!5. 
Calculation  of  change  of  volume  of  gas,  §5 

p49. 
Calculations  in  ventilation,  §13,  p34. 

Special  ventilation,  §13,  p49. 
Calorie,  French,  §5,  p!8. 

Pound,  §5,  pJ8. 

Calorific  value  of  fuels,  §16,  p90. 
Calorimeter,  §16,  p90. 

Mahler's  bomb,  §16,  p90. 
Cannel  coal,  §16,  p!4. 
Canvas  door,  §13,  p4. 
Capell  fan,  §15,  p25. 
Car-dumping  machine,  Brown,  §16,  pl!8. 

machine,  McMyler,  §16,  p!20. 

machines,  §16,  pi  18. 
Carbon,  §16,  pi. 

dioxide,  -§6,  p3. 

dioxide,  Effect  of,  on  firedamp,  §6,  p9. 

dioxide,  Explanation  of  term,  §5,  p41. 

fixed,  Determination  of,  in  coal,  J16,  p93. 

fixed,  and  ash,  Determination  of,  in  coal, 
§16,  p93. 

monoxide,  §6,  p2. 

monoxide.  Effect  of,  on  firedamp,  §6,  p9. 

monoxide,   Explanation  of  term,   §5,   p41. 
Carbonic  acid.  Explanation  of  term,  §5,  p41. 

acid  gas,  §6,  p3. 

acid  gas,  Effect  of,  on  firedamp,  §6,  p9. 

oxide,  §6,  p2. 

oxide,  Effect  of,  on  firedamp,  §6,  p9 


INDEX 


Carbonic — (Continued) 

oxide,  Explanation  of  term,  §5,  p41. 
Carbureted  hydrogen,  §6,  p2. 
Carriers,  Bucket,  §16,  p!09. 
Casing,  Expansion  of  fan,  §15,  p38. 
Celsius  scale,  §5,  p!4. 
Centigrade  scale,  §5,  p!4. 
Centrifugal  fan,  Principle  of  action  of,  §15,  p6. 

fan,  Static  pressure  due  to  a,  §15,  p44. 

fans,  §15,  p5. 

fans,  Advantage  of,  §15,  p52. 

fans,  Types  of,  §15,  p21. 

force  developed  by  revolution  of  fan,  §15, 
p32. 

force  of  fan.  Work  of.  §15.  P33. 
Change   of  pressures  due  to  the  change  of 
volume,  §5,  p50. 

of  volume  of  gases  due  to  chemical  changes, 

§5.  P49. 
Charcoal,  §16,  pll. 

Uses  of,  §16,  pll. 
Chemical  compounds,  §5,  p41. 

equations.  §5,  p46. 

equations,  Writing,  §5,  p47. 

formula,  §5,  p42. 

reactions,  §5,  p46. 

reactions,  Heat  of,  §5,  p53. 
Chemistry,  §5,  p38. 

of  combustion,  §16,  p69. 

of  gases,  §5,  p38. 
Chimney,  Fan,  §15,  p!2. 
Chokedamp,  §6,  p4. 
Chute,  Adjustable,  §16,  pl!5. 
Chutes,  §16,  pl!5. 

Pitch  of,  §16,  pi  15. 
Circulation  of  air,  Factors  of  a,  §13,  p!6. 

Quantity  of  air  in,  §13,  p!7. 
Circulations,  §13,  p46. 

Comparing  different,  §13,  p52. 
Clam-shell  bucket,  516,  p98. 
Clanny  lamp,  §6,  p41 

Bonneted,  §6,  p42. 
Closed-running  fans,  §15,  p6. 
Clowes  hydrogen  lamp,  §6,  p50. 
Coal,  §16,  p!3. 

Analysis  of.  §16,  p91. 

analysis,  Notes  for,  §16,  p96. 

analysis,  Report  of,  §16,  p97. 

Ash  in,  §16,  p!8. 

Caking  and  non-caking,  §16,  p!5. 

Cannel.  §16.  p!4. 

Coking.  §16,  pi  5. 

Composition  of,  §16,  p!8. 

Determination  of  fixed  carbon  and  ash  in, 
§16,  p93. 

Determination  of  moisture  in,  §16,  p92. 

Determination  of  sulphur  in,  §16,  p94. 


Coal — (Continued) 

Determination     of     volatile     combustible 
matter  in,  §16,  p93. 

dust  as  fuel,  §16,  p36. 

-dust  burner,  §16,  p37. 

dust,  Effect  of,  on  firedamp,  §6,  p9. 

dust,  Effect  of,  on  flame  of  lamp,  §6.  p22. 

Free-burning,  §16,  p!6. 

gas,  §16.  p6. 

gas,  purified,  Average  composition  of,  §16, 
P63. 

Hard.  §16.  p!4. 

Hoisting,  conveying,  and  storing,  §16,  p97. 

Long-flaming  and  short-flaming,  §16,  p!5. 

Market  value  of,  §16,  p31. 

Moisture  in,  §16,  p!8. 

Origin  of,  §16,  p!3. 

piles,  Extinguishing  fires  in,  §16,  p35. 

piles,  Fires  in,  §16,  p35. 

sampling  for  analysis,  §16,  p92. 

Relation  of  heating  value  of,  to  composi- 
tion of  combustible,  §16,  p23. 

Sea,  §16,  p!8. 

Selling,  by  analysis,  §16,  p30. 

Soft,  §16,  p!4. 

Spontaneous  ignition  of,  §16,  p32. 

Storage,  §16,  p!21. 

storage,  Bridge  tramway  system  of,   §16, 
p!24. 

storage,  Dodge  revolving  system  of,   §16 
p!29. 

storage,  Dodge  system  of,  §16,  p!26. 

storage.  Side-hill,  §16.  p!22. 

storage,  Trestle,  §16,  p!23. 

Ultimate  analysis  of,  §16,  p96. 

Weathering  of,  §16,  p31. 
Coals,  Blacksmith,  §16,  p!7. 

Classification  of,  §16,  p!4. 

Domestic,  §16,  p!7. 

Gas,  §16,  pp!7,  62. 

Relative  practical  values  of  steam,  §16  p26. 

Steam,  §16,  p!6. 

Valuation  of,  as  fuel,  §16,  p23. 

Valuing  of,  by  test  and  by  analysis,  §16 

P28. 
Coefficient,  §5,  p40. 

of  friction.  Value  of,  §13,  p!9. 
Coefficients  of  expansion,  §5,  p25. 
Cohesion,  §5,  pi. 
Coke,  §16,  p40. 

Analysis  of,  §16,  p91. 

Definition  of,  §16,  p!5. 
Coking  coal,  §16,  p!5. 
Column.  Motive,  §14.  p40. 
Columns,  Air,  §14,  p38. 

Density  of  air,  §14.  p49. 
Combined  dust  and  gas  explosion,  §6,  p25. 


xii 


INDEX 


Combustible  elements,  §16.  pi. 

matter.  Volatile,  §16,  p7. 

matter,  volatile.  Determination  ot,  in  coal, 
§16.  p93. 

Relation  of  heating  value  of  coal  to  composi- 
tion of.  §16,  p23. 

substance,  §5,  p55. 
Combustion,  §5,  p54. 

Chemistry  of,  §16.  p69. 

Dulong's  formula  for  heat  of,  §16.  p85. 

Heat  of,  §5.  p54;  §16,  p85. 

Lord  and  Haas's  formula  for  heat  of,  §16, 
P86. 

of  fuel,  §16,  p69. 

Spontaneous,  §5,  p58. 

Comparing  different  circulations,  §13,  p52. 
Composition  of  a  fuel,  Methods  of  expressing 
the,  §16.  p4. 

of  the  atmosphere,  §5,  p51. 

percentage,  §5,  p44. 
Compound,  Definition  of,  §5,  p38. 

gas,  Calculating  heating  value  of  a,  §  16,  p87. 
Compounds,  Chemical,  §5,  p41. 
Condition  of  air  in  mines,  §6,  p!5. 
Conduction,  §5,  p!3. 
Convection,  §5,  p!3. 
Conveyer,  Bucket,  §16,  pl!2. 
Conveyers,  §16,  p!04. 

Belt,  §16,  p!06. 

Flight,  §16,  p!04. 

Conveying  and  hoisting  systems,  Combina- 
tions of,  §16,  pi  17. 

Coal,  §16,  p97. 
Cowl,  Wind,  §15,  p3. 
Crane,  Locomotive,  §16,  plOO. 

Overhead,  §16.  p!03. 
Cranes,  §16,  plOO. 
Crossings,  Air,  §13,  p7. 
Cubical  expansion,  §5,  p25. 
Culm,  Sealing  off  with,  §5,  p67. 
Curtain,  §13,  p4. 

D 

Dangerous  atmosphere,  §6,  p!6. 
Davy  lamp,  §6,  p37. 

lamp,  Bonneted,  §6,  p39. 

lamp,  Fire-boss,  §6,  p38. 

lamp,  Jack,  §6,  p39. 

lamp.  Testing  for  gas  with,  §6,  p62. 

lamp,  Tin-can,  §6,  p39. 

Decomposition,  Heat  absorbed  by,  §16,  p88. 
Deflector,  Howat,  §6,  p43. 
Density,  §5,  p2. 

and  specific  gravity  of  gases,  §5,  p52. 

of  air  columns,  §14,  p49. 

of  air  referred  to  oxygen,  §5,  p52. 

of  any  gas,  Rule  for  finding,  §5.  p46. 


Density — (Continued) 

of  mine  gases,  §5,  p46. 
Derrick,  Fixed  steel,  §16,  p!03. 
Determination  of  specific  gravity  of  solids  by 
a  balance,  §5,  p6. 

of  specific  gravity  of  solids  by  a  specific- 
gravity  bottle  and  balance,  §5,  p7. 
Determining  specific  gravity,  §5,  p6. 

specific  gravity  by  the  hydrometer,  §5,  p9. 

specific  gravity  of  liquids  by  balance,  §5,  p8. 

the  specific  gravity  of  gases,  §5.  pll. 
Diffusion  of  gases,  §5,  p59. 

Rate  of,  §5,  p60. 

Dip  and  rise  of  workings,  §14,  p48. 
Disk  fans,  §15,  p4. 
Division,  Proportionate,  §14,  p20. 
Dodge  revolving  bridge  system  of  storage,  §16. 
p!29. 

system  of  coal  storage,  §16,  p!26. 
Domestic  coals,  §16,  p!7. 
Door,  Canvas,  §13,  p4. 

regulator,  §13,  p5. 
Doors,  Explosion,  §15,  p20. 

Mine,  §13,  p3. 
Downcast  shaft,  §13,  p2. 
Drift,  Dumb,  §14,  p52. 

mine.  Ventilation  of  a,  §14,  p26. 
Drop-bottom  bucket,  §16,  plOO. 
Dulong's  formula,  §16,  p85. 
Dumb  drift,  §14,  p52. 

Dust,  coal,  Effect  of,  on  flame  of  lamp,  §6 
P22. 

explosion,  §6,  p23. 
Dynamite,  Exploding,  §5,  p66 


Effect  of  rate  of  transpiration,  §5,  p63. 
Efficiency  of  fans,  Manometrical,  §15,  p44. 

of  fans,  Mechanical,  §15,  p45. 

of  mine  furnace  compared  with  fan,  §15 

p53. 

Electric  lamps,  Portable,  §6,  p77. 
Element,  Definition  of  an,  §5,  p38. 
Elements,  Combustible,  §16,  pi. 
Elevators,  Bucket,  §16,  pi  10. 
Engines,  Use  of  gas  in  gas,  §16,  p68. 
Entering  a  mine  after  an  explosion,  §6,  p30. 
Equations,  Chemical,  §5,  p46. 

Writing  chemical,  §5,  p47. 
Equivalent  orifice,  §15,  p51. 
Eschka  mixture,  §16,  p96. 
Ethene,  §6,  p4. 
Ethylene,  §6,  p4. 

Effect  of,  on  firedamp,  §6,  p9. 
Evan  Thomas  lamp,  §6,  p43. 
Exhaust  fan,  §15,  p7. 

system  of  ventilation,  §13,  p!5. 


INDEX 


Xlll 


Expansion,  Coefficients  of,  §5,  p25. 

Cubical,  §5,  p25. 

Formula  for  calculating,  §5,  p26. 

Linear,  §5,  p25. 

of  bodies  by  heat,  §5.  p25. 

Surface.  §5,  p25. 
Exploding  dynamite,  §5,  p66. 
Explosion,  Advance  of  a  mine,  §6,  p27. 

Arrest  of  an,  §6,  p28. 

doors,  §15.  p20. 

Dust,  §6,  p23. 

Gas,  §6,  p22. 

of  combined  gas  and  dust,  §6,  p25. 

of  hiethane  (marsh  gas),  Initial  force  of  an, 
§5,  P57. 

Recoil  of  an,  §6,  p28. 

Reducing  the  liability  to,  §6,  p33. 

Transmission  of  flame  of  initial,  §6,  p26. 
Explosions,  Entering  a  mine  after,  §6,  p30. 

Mine,  §6,  p22. 

Phenomena  of,  §6,  p26. 

Prevention  of,  §6,  p33. 

Types  of,  §6,  p22. 
Explosive  condition  of  mine  air,  §6,  p!5. 

limits  of  firedamp,  §96,  p8. 
Expressing  a  molecule  by  symbols,  §5,  p42. 
Extinction  of  oil  and  gas  flames,  §6,  p20. 
Extinctive  character  of  an  atmosphere,  §6, 


Factors  of  a  circulation  of  air,  §13.  p!6. 

Fahrenheit  scale,  §5,  p!4. 

Fan  blades,  Support  of,  §15,  p7. 

blades,  Tapered,  §15.  p41. 

Blow-down,  §15,  p7. 

Blower,  §15,  p7. 

Breadth  of,  §15,  p30. 

Calculation  of  water  gatige  due  to  action 
of,  §15,  p42. 

calculations,  §15,  p42. 

Capell,  §15,  p25. 

casing,  Expansion  of,  §15,  p28. 

casing  or  housing,  §15,  p9. 

Centrifugal  force  developed  by  revolution 
of,  §15,  p32. 

chimney,  §15,  p!2. 

Connection   of,   with    mine   opening,    §15, 
p!6. 

construction,  Details  of,  §15,  p7. 

designs,  §15,  p28. 

Efficiency  of  mine  furnace  compared  with, 
§15,  p53. 

Exhaust,  §15.  p7. 

Force,  §15,  p7. 

Guibal,  §15.  p21. 

Mechanical  efficiency  of,  §16,  p46. 

Nasmyth,  §15,  p21. 


Fan— (Continued) 

Open-running,  §15,  p6. 

Outer  diameter  of,  §15,  p36. 

pit  and  foundation,  §15,  p!4. 

Power  required  by,  §15,  p35. 

Propeller,  §15,  p4. 

Quantity  of  air  delivered  by,  §15,  p35. 

Robinson,  §15,  p27. 

Schiele.  §15,  p24. 

Shutter,  §15,  p!3. 

Sirocco,  §15,  p27. 

Size  of  intaking  opening  of,  §15.  p29. 

Static  pressure  due  to  a  centrifugal,  §15, 
p44. 

Volume  of,  §15,  p31. 

Waddle,  §15,  p23. 

Work  of  centrifugal  force  of,  §15,  p33. 
Fans,  Advantages  of  centrifugal,  §15,  p52. 

Centrifugal,  §15,  p5. 

Closed-running,  §15,  p6. 

Curvature  of  blades  of,  §15,  p39. 

Disk,  §15,  p4. 

Guide  blades  of,  §15,  p41. 

Inclination  of  blades  of,  §15,  p40. 

Manometrical  efficiency  of,  §15,  p44. 

Number  of  blades  of,  §15,  p28. 

Principal  of  action  of  centrifugal.  §15,  p6. 

Secondary  blades  of,  §15,  p39. 

Types  of  centrifugal,  §15,  p21. 

Ventilating,  §15,  p3. 
Fatal  atmosphere,  §6,  p!6. 
Feeders  and  blowers,  §5,  p53. 
Fire-boss  Davy  lamp,  §6,  p38. 
Fire,  Extinguishing  a  coal-pile,  §16,  p35. 

grate    surface,   Area   of,   in  a   ventilating 
furnace,  §14,  p58. 

Temperature  of,  §16,  p79. 

Temperature  of    the,  the  fuel  containing 

hydrogen  and  water,  §16,  p82. 
Firedamp,  §6,  p7. 

Effect  of  other  gases  and  dust  on,  §6,  p9. 

Effect  of  pressure  and  temperature  on,  §6, 
P9. 

Explosive  ranges  of,  §6,  p8. 
Fires,  Gob,  §5,  p65. 

in  coal  piles,  §16,  p35. 

Treatment  of  gob,  §5,  p65. 
Fixed  carbon,  §16,  p7. 

carbon  and  ash,  Determination  of,  in  coal, 

§16.  p93. 

Flame   cap   corresponding   to   different   per- 
centages of  gas,  Height  of,  §6,  p64. 

of  blasting  powder.  Temperature  of,  §6,  pi  3 

of  burning  gas,  Temperature  of,  §6,  pl3. 

of  lamp.  Effect  of  coal  dust  on,  §6,  p22. 

Transmission  of,  of  initial  explosion,   56, 


xiv 


INDEX 


Flames,  Extinction  of  oil  and  gas,  §6  p20. 
Flashdamp,  §6,  p8. 

Flat  seam,  Ventilation  of  long- wall  mine  in, 
§14.  p31. 

seams,  Ventilation  of  slope  or  shaft  mines 

in,  §14.  P28. 

Flight  conveyers,  §16,  p!04. 
Flooding  a  mine,  §5,  p67. 
Force,  Centrifugal,  developed  by  revolution 
of  fan,  §15,  p32. 

fan,  §15,  p7. 

Initial,  of  an  explosion  of  methane  (marsh 
gas),  §5,  p57. 

of  fan,  Work  of  centrifugal,  §15,  p33. 
Forces,  Natural,  §5,  pi. 
Form  and  size  of  airways,  §13,  p9. 
Forms  of  airways,  Comparison  of,  §13,  pll. 

of  matter,  §5,  p!2. 
Formula,  Chemical,  §5,  p42. 

Dulong's,  §16,  p85. 

Lord  and  Haas's,  §16,  p86. 
Formulas,  Elementary  ventilation,  §13,  p35. 

for  calculating  expansion,  §5,  p26. 

Transposition  of,  §13,  p36. 
Forter  water-seal  producer,  §16,  p58. 
Foundation,  Fan,  §15,  p!4. 
Free-burning  coal,  §16,  p!6. 
French  calorie,  §5,  p!8. 
Friction,  Coefficient  of,  §13,  p!9. 

Value  of  coefficient  of,  §13,  p!9. 
Fuel,  Advantages  and  disadvantages  of  petro- 
leum as  a,  §16,  p41. 

Ash  in,  §16,  P3. 

burned  in  air,  §16,  p72. 

Coal  dust  as,  §16,  p36. 

Combustion  of,  §16,  p69. 

containing  hydrogen  and  water,  Available 
heating  value  of,  §16,  p89. 

Distribution  of  gaseous,  §16,  p67. 

employed  in  making  producer  gas,  §16,  p58. 

Machines  for  briqueting,  §16,  p39. 

Methods  of  expressing  the  composition  of, 
§16,  P4. 

Practical  values  of,  for  different  uses;  §16, 
p25. 

Pressed,  §16,  p38. 

Uses  of  gaseous,  §16,  p67. 

Valuation  of  coals  as,  §16,  p23. 

Value  of  wood  as,  §16,  p9. 
Fuels,  Calorific  value  of,  §16,  p90. 

Composition  and  classification  of,  §16,  pi. 

Gaseous,  §16,  p52. 

Impurities  in,  §16,  p3. 

Liquid,  §16,  p41. 

Moisture  in,  §16,  p3. 

Properties  of,  §16,  pi. 

Solid,  §16,  p8. 


Furnace,    Area    of    fire-grate    surface    in    a 

ventilating,  §14,  p58. 
Coal  burned  per  hour  in  a  ventilating,  §14, 

P57. 

Construction  of  a  mine,  §14,  p51. 
Efficiency  of  mine,  compared  with  fan,  §15, 

P53. 

Power  of  a  mine,  §14,  p54. 
Pressure  due  to,  §14,  p53. 
ventilation,  §14,  p50. 
ventilation,  Temperature  of  air  in,  §14,  p55. 

G 

Gas  and  dust  explosion,  Combined,  §6,  p25. 
Approaching  a  body  of,  §6,  p63. 
Average  composition  of  purified  coal,  §16, 

P63. 

Calculating  the  heating  value  of  a  com- 
pound, §16,  p87. 
Calculation  of  change  of  volume  of  a,  §5, 

p49. 
Change  of  pressure  of,  due  to  the  change  of 

volume,  §5,  p50. 
Coal,  §16,  p60. 
coals,  §16,  pp  17,  62. 
engine,  Use  of  gas  in,  §16,  p68. 
explosion,  §6,  p22. 
flames.  Extinction  of,  §6,  p20. 
Fuel  employed  in  making  producer,  §16, 

P58. 
Ignition  of  mine,  by  incandescent  lamps, 

§6,  P14. 

indicators,  §6,  p67. 
Lamps  for  testing  for,  §6,  p37. 
Producer,  §16,  p56. 

purified  water,  Composition  of,  §16,  p64. 
Rule  for  finding  the   density  of  any,  §5, 

p46. 

Temperature  of  flame  of  burning,  §6,  p!3. 
Testing  for,  §6,  p62. 

Testing  for,  by  the  Shaw  machine,  §6,  p72. 
-testing  machine,  Shaw,  §6,  p71. 
Use  of,  in  gas  engines,  §16,  p68. 
Water.  §16,  P63. 
water,  Impurities  in,  §16,  p64. 
Gaseous  fuel,  Distribution  of,  §16,  p67. 
fuel,  Uses  of,  §16,  p67. 
fuels,  §16,  p52. 

mines.  Ventilation  of,  §14,  p35. 
Gases,  §5,  p!2. 

Causes  of  ignition  of  mine,  §6,  p!3. 
Change    of    volume    of,    due  to    chemical 

changes,  §5,  p49. 
Chemistry  of,  §5,  p38. 
common  to  mines,  §6,  pi. 
Density  and  specific  gravity  of,  §5,  p52. 
Density  of  mine,  §5  p46. 


INDEX 


xv 


Gases — (Continued) 

Diffusion  of,  §5.  p59. 

Ignition  of,  §6,  p!2. 

Inflammable  mine,  §6,  p!2. 

in  mines,  Testing  for,  §6,  p36. 

Mixture  of,  §5,  p36. 

Mixtures    of    equal    volumes    of,    having 
unequal  pressures,  §5,  p36. 

Mixtures  of  mine,  §6,  p7. 

Mixtures  of,  of  the  same  temperature  and 
pressure,  §5,  p36. 

Mixtures  of  two,  having  unequal  volumes 
and  pressures,  §5,  p37. 

Occlusion  of,  §5,  p60. 

Physics  of,  §5,  pi. 

Pressure  of  occluded,  §5,  p61. 

Properties  of  mine,  §5,  p59. 

Temperature  and  pressure  of,  §5,  p35. 

Transpiration  of,  from  coal,  §5,  p62. 

Volume  and  pressure  of,  §5,  p34. 

Volume  of,  §5,  p27. 

Volume,  temperature,  and  pressure  of,  §5, 
p34. 

Weight  and  volume  of,  §16,  p72. 
Gauge  for  safety  lamp,  .§6,  p57. 

Pressure,  §5,  p33. 

Vacuum,  §5,  p32. 

Water,  §13,  p31. 
Gay-Lussac's  law,  §5,  p28. 
Geordie  lamp,  §6,  p41. 
Gob  fires,  §5,  p65. 
Guibal  fan,  §15,  p21. 
Guide  blades  of  fans,  §15,  p41. 

H 

Heat,  §5.  p!2. 

absorbed  by  decomposition,  §16,  p88. 
Expansion  of  bodies  by,  §5,  p25. 
Latent,  §5,  p23 

Mechanical  equivalent  of,  §5,  p!8. 
of  chemical  reactions,  §5,  p53. 
of  combustion,  §16,  p85;  §5,  p54. 
of  combustion,  Dulong's  formula  for,  §16, 

p85. 
of  combustion,  Lord  and  Haas's  formula 

for,  §16,  p86. 
Quantity  of,  §5,  p!8 
Sensible,  §5,  p!9. 
Sources  of,  §5,  p!3. 
Specific,  §5.  p!9. 
Total,  §5,  p24. 
Transmission  of,  §5,  p!3. 
units,  §5,  p!8. 
Heating  value  of  a  compound  gas.  Calculating 

the.  §16,  p87. 
value  of  coal,  Relation  of,  to  composition 

of  combustible,  §16,  p23. 


Heating — (Continued) 

value    of    fuel    containing    hydrogen    and 
water.  Available.  §16,  p89. 

value  of  petroleum,  §16,  p41. 
Helmet,  Vajen-Bader,  §6,  p32. 
Hoisting  and  conveying  systems,   Combina- 
tions of,  §16,  pi  17. 

coal,  §16,  p97. 
Horizontal  pressure  of  coal  against  retaining 

walls.  Determining.  §16,  p!31. 
Horsepower,  §J3,  p24. 
Houses,  Safety-lamp,  §6,  p73. 
Howat  deflector,  §6,  p43. 
Humidity  of  air.  Relative,  §16,  p74. 
Hunt  automatic  railway,  §16,  p!03. 
Hydrogen,  §6,  p6;  §16,  p2. 

Maximum  theoretical  temperature  of  the 
fire  due  to  burning,  in  dry  air,  §16,  p80. 

sulphide,  §6,  p4. 
Hydrometer,  Beaume's,  §5,  pll. 

Determining  specific  gravity  by  the,  §5,  p9. 

Nicholson's.  §5.  p9. 


Incandescent  lamps,  Ignition  of  mine  gas  by. 

§6,  P14. 
Indicator,  Beard-Mackie  sight,  §6,  p68. 

Liveing,  §6,  p68. 
Indicators  for  gas,  §6,  p67. 
Initial    force    of    an    explosion    of   methane 

(marsh  gas),  §5,  p57. 
Ignition  of  coal,  Spontaneous,  §16,  p32. 

of  gases,  Temperature  of,  §6,  p!2. 

of  mine  gas  by  incandescent  lamps,  §6,  pi  4. 

of  mine  gases,  Causes  of,  §6,  p!3. 

Temperature  of,  §16,  p78. 
Illuminating  power  of  oils,  §6,  p60. 

power  of  safety  lamps,  Relative,  §6,  p61. 
Impurities  in  fuels,  §16,  p3. 
Inclined  seams.  Ventilation  of,  §14,  p32. 
Inflammable  mine  gas.  §6,  p!2. 
Intake,  Definition  of,  §13,  p2. 


Jack  Davy  lamp,  §6,  p39. 


Kent's  method  for  determining  moisture  ir 
coal,  §16,  P92. 

L, 

Lamp,  Bonneted  Clanny,  §6,  p42. 
Bonneted  Davy,  §6,  p39. 
Bonneted  Marsaut,  §6,  p47. 
Bonneted  Mueseler,  §6,  p45. 
Clanny,  §6,  p41. 
Clowes  hydrogen,  §6,  p50. 


INDEX 


Lamp — (Continued) 

Davy,  §6.  p37. 

Evan  Thomas.  §6,  p43. 

gauge,  §6,  p57. 

Geordie,  §6,  p41. 

Jack  Davy,  §6,  p39. 

Marsaut,  §6,  p46. 

Mueseler.  §6.  p44. 

Pieler,  §6,  p52. 

Pocket  Davy,  §6,  p38. 

Principle  of  the  safety,  §6,  p35. 

Stevenson,  §6,  p41. 

Stokes,  §6,  p51. 

Tin-can  Davy,  §6,  p39. 

Wicks,  §6,  p56. 

Wolf,  §6,  p48. 
Lamps,  Ashworth-Hepplewhite-Gray,  §6,  p47. 

.for  general  use,  Safety,  §6,  p37. 
'for  testing  for  gas,  §6,  p37. 

Portable  electric,  §6,  p77. 

Special,  §6,  p47. 

Types  of  safety,  §6,  p36. 
Latent  heat,  §5,  p23. 
Laughing  gas,  §6,  p5. 
Lead-plug  lock,  §6,  p53. 
Linear  expansion,  §5,  p25. 
Liquid  fuels,  §16,  p41. 
Liquids,  §5,  p!2. 
Liveing  indicator,  §6,  p68. 
Loading  out,  §5,  p66. 
Lock,  Lead-plug,  §6,  p53. 
Locks  for  safety  lamps,  §6,  p52. 

Magnetic,  §6,  p54. 
Locomotive  crane,  §16,  plOO. 
Long-flaming   and    short-flaming    coal,    §16, 

pl& 
Long-wall  mine  in  flat  seam,  Ventilation  of  a, 

§14,P31. 
Lord  and  Haas's  formula,  §16,  p86. 

M 

Machines,  Car-dumping,  §16,  pi  18. 

for  briqueting  fuel,  §16,  p39. 
Magnetic  locks,  §6,  p54. 
Mahler's  bomb  calorimeter,  §16,  p90. 
Manometrical  efficiency  of  fans,  §15,  p44. 
Mariotte's  law,  §5,  p34. 
Marsaut  lamp,  §6,  p46. 

lamp,  Bonneted,  §6,  p47. 
Marsh  gas,  §6,  p2. 
Mass  and  volume,  §5,  pi. 
Masses,  §5,  pi. 
Matter,  §5,  pi. 

Forms  of,  §5,  p!2. 

McMyler  car-dumping  machine,  §16,  p!20. 
Measurement  of  atmospheric  pressure,  §5,  p29. 

of  temperature,  §5,  p!3. 


Measurements,  Air,  §13,  p25. 
Mechanical  efficiency  of  a  ventilator,  Effect 
of  mine  resistance  on,  §15,  p49. 

efficiency  of  fans,  §15,  p45. 

equivalent  of  heat,  §5,  p!8. 

mixtures,  §5,  p41. 

ventilation,  §15,  pi. 
Mercurial  barometer,  The,  §5,  p30. 
Methane,  §6.  p2. 

(marsh  gas).  Initial  force  of  the  explosion 

of,  §5,  p57. 
Mine  air,-  Explosive  condition  of,  §6,  p!5. 

doors,  §13,  p3. 

explosion,  Advance  of  a,  §6,  p27. 

explosions,  §6,  p22. 

furnace,  Construction  of  a,  §14,  p51. 

furnace,  Efficiency  of,  compared  with  fans, 
§15,  p53. 

furnace.  Power  of  a,  §14,  p54. 

gas,  Ignition  of,  by  incandescent  lamps,  §6, 
p!4. 

gases,  Causes  of  ignition  of,  §6,  p!3. 

gases,  Density  of,  §5,  p46. 

gases,  Inflammable,  §6,  p!2. 

gases,  Mixtures  of,  §6,  p7. 

gases,  Physical  properties  of,  §5,  p59. 

long-wall  in  flat  seams,  Ventilation  of  a,  §14, 
P31. 

opening,  Connection  of  fan  with,  §15,  p!6. 

resistance,  Definition  of,  §13,  p!7. 

resistance,   Effect   of,   on   mechanical   effi- 
ciency of  a  ventilator,  §15,  p49. 

ventilation,  General  principles  of,  §13,  pi. 

ventilation,   Influence  of  seasons  on,   §14, 
p45. 

Ventilation  of  a,  §14,  p24. 

Ventilation  of  a  drift,  §14,  p26. 
Mineral  oil,  §6,  p58. 
Mines,  Condition  of  air  in,  §6,  p!5. 

Gases  common  to,  §6,  pi. 

Means  for  ventilating,  §14,  p37. 

slope,  or  shaft,  Ventilation  of,  in  flat  seams, 
§14,  p28. 

Ventilation  of  different  types  of,  §14,  p26. 

Ventilation  of  gaseous,  §14,  p35. 
Mixture  of  gases,  §5,  p36. 
Mixtures  of  mine  gases,  §6,  p7. 

Mechanical,  §5,  p41. 

of  equal  volumes  of  gases  having  unequal 
pressures,  §5,  p36. 

of  gases  of  the  same  temperature  and  pres- 
sure, §5,  p36. 

of  two  gases  having  unequal  volumes  and 

pressures,  §5,  p37. 
Moisture,  §16,  p3. 

in  coal,  §16,  p!8. 

in  coal,  Determination  of,  §16,  p92. 


INDEX 


xvn 


Molecular  weight.  §5,  p43. 
Molecule,  Expressing  a,  by  symbols,  §5,  p42. 
Molecules,  §5.  pi. 
Motive  column,  §14,  p40. 
Mueseler  lamp,  §6,  p44. 
lamp.  Bonneted,  §6,  p45. 

N 

Nasmyth  fan,  §15,  p21. 
Natural  forces,  §5,  pi. 

splitting,  Calculations  in,  §14,  plO. 

ventilation,  §13,  p!4;  §14,  p37. 
Nicholson's  hydrometer,  §5,  p9. 
Nitrogen/  §6,  p5. 

Effect  of,  on  firedamp,  §6,  p9. 
Nitrous  oxide,  §6,  p5. 
Non-caking  coal,  §16,  p!5. 

O 

Occluded  gases,  Pressure  of,  §5,  p61. 

Occlusion  of  gases,  §5,  p60. 

Oil  flames,  Extinction  of,  §6,  p20. 

Mineral,  §6,  p58. 
Oils,  Animal,  §6,  p58. 

for  safety  lamps,  §6,  p57. 

Relative  illuminating  powers  of,  §6,  p60. 

Vegetable,  §6,  p57. 
Olefiant  gas,  §6,  p4. 

gas,  Effect  of,  on  firedamp,  §6,  p9. 
Open-running  fans,  §15,  p6. 
Orange-peel  bucket,  §16,  p99. 
Orifice,  Equivalent,  §15,  p51. 
Outbursts,  §5,  p64. 
Overcasts,  §13,  p7. 
Overhead  crane,  §16,  p!03. 
Oxidation,  §5,  p54. 
Oxygen,  §6,  p6. 


Partial  vacuum,  §5,  p30. 
Peat,  §16,  p!2. 

Composition  of,  §16,  p!2. 
Percentage  composition,  §5,  p44. 
Perimeter  of  airway,  Relation  between,  and 

power,  §13,  p54. 
Petroleum,  §6,  p58;  §16,  p41. 

as  a  fuel,  Advantages  and  disadvantages 
of,  §16,  p41. 

Composition  of,  §16,  p43. 

Heating  value  of,  §16,  p41. 

Method  of  burning,  §16,  p46. 

Uses  of,  §16,  p46. 
Phenomena  of  explosions,  §6,  p26. 
Physical  properties  of  mine  gases,  §5,  p59. 
Physics  of  gases,  §5,  pi. 
Picker  for  wicks,  §6.  p56. 
Pieler  lamp,  §6,  p52. 
145—35 


Pit.  Fan,  §15.  p!4. 

Pitch  of  chutes,  §16,  pi  15. 

Plenum  system  of  ventilation,  §13,  p!5. 

Pocket  Davy  lamp,  §6,  p38. 

Portable  electric  lamps,  §6,  p77. 

Pound  calorie,  §5,  p!8. 

Power,  §13,  p24. 

and  work  in  producing  an  air-current,  §13, 
P22. 

of  a  mine  furnace,  §14,  p54. 

on  the  air,  §13,  p24. 

ratio    for   similar   airways,    General,    §13, 
p67. 

ratio,  General,  §13,  p56. 

Relation  between  area  of  airway  and,  §13, 
p55. 

Relation  between  perimeter  of  airway  and, 
§13.  p54. 

Relation  between  the  length  of  an  airway 
and  the,  §13,  p54. 

Relation  of  velocity  or  quantity  of  air  to, 
§13,  p55. 

required  by  fan,  §15,  p35. 
Pressed  fuel,  or  briquets,  §16,  p38. 
Pressure,  §13,  p60. 
•  Absolute,  §5,  p31. 

against  retaining  walls.  Determining  hori- 
zontal, §16,  p!31. 

and  volume  of  gases,  §5,  p34. 

Atmospheric,  §5,  p28. 

Calculation    of    unit    of   ventilating,    §13, 
P22. 

due  to  a  furnace,  §14,  p53. 

Effect  of,  on  firedamp,  §6,  p9. 

gauge,  §5,  p33. 

of  occluded  gases,  §5,  p61. 

ratio   for   similar   airways.  General,    §13, 
P67. 

ratio,  General,  §13.  p60. 

Static,  due  to  a  centrifugal  fan,  §15,  p44. 

To  measure  the  ventilating,  §13,  p31. 

Ventilating,  §13,  p!4. 
Pressures,  Change  of,  due  to  the  change    01 

volume,  §5,  p50. 

Preventions  of  explosions,  §6,  p33. 
Principle  of  the  safety  lamp,  §6,  p35. 
Problems,  Practical  ventilation,  §13,  p39. 
Producer.  Porter  water-seal,  §16,  p58. 

gas,  §16,  p56. 

gas,  Fuel  employed  in  making,  516,  p58. 

Operation  of  the,  §16,  p60. 

reactions,  §16,  p59. 
Propeller  fan,  §15,  p4. 
Properties  of  fuels,  §16,  pi. 
Proportionate  division,  §14,  p20. 

splitting,  514.  p20. 
Proximate  analysis.  §14,  p91 ;  §16,  p4. 


INDEX 


Quantity  and  velocity  of  air  required,  §14, 

P24. 

of  air  in  circulation,  §13,  p!7. 
of  air  required  by  law,  §14,  p25. 
of  heat,  §5,  p!8. 


Radiation,  §5,  p!3. 
Railway,  Hunt  automatic,  §16,  103. 
Rate  of  diffusion,  §5,  p60. 
Reactions,  Chemical,  §5,  p46. 

Producer,  §16,  p59. 
Reaumur  scale,  §5,  p!5. 
Recoil  of  an  explosion,  §6,  p28. 
Reduction,  §5,  p54. 
Regulator  door,  §13,  p5. 
Regulators,  §13,  p4. 
Relative  illuminating  power  of  safety  lamps, 

§6,  P61. 

Repulsion,  §5,  pi. 
Rescue  appliances  and  mine  supplies,  §6,  p31. 

work,  §6,  p30. 
Resistance,  Mine,  §13,  p!7. 

of  an  airway,  Calculation  of  the,  §13,  p20. 
Value  of  unit  of,  §13,  p!9. 
Retorts,  Operating  a  bench  of,  §16,  p61. 
Return,  Definition  of  the,  §13,  p2. 
Reversing  the  air-current,  §15,  p!7. 
Revolving  bridge  system  of  storage,  Dodge 

§16,  p!29. 

Rise  and  dip  of  workings,  §14,  p48. 
Robinson  fan,  §15,  p27. 
Rubbing  surface  of  an  airway,  §13,  pll. 
Rule  for  calculating  total  heat  absorbed  by 

any  substance,  §5,  p24. 

for  changing  centigrade  temperatures  into 

corresponding  Fahrenheit  values,  §5,  p!5. 

for  changing  centigrade  temperatures  into 

corresponding  Reaumur  values,  §5,  p!6. 

for  changing  Fahrenheit  temperatures  into 

corresponding  centigrade  values,  §5,  p!5. 

for  changing  Fahrenheit  temperatures  into 

corresponding  Reaumur  values,  §5,  p!6. 

for  changing  Reaumur  temperatures  into 

corresponding  centigrade  values,  §5,  p!6. 

for  changing  Reaumur  temperatures  into 

corresponding  Fahrenheit  values,  §5,  p!5. 

for  converting  centigrade  temperatures  into 

absolute  temperatures,  §5,  p!8. 
for    converting    Fahrenheit    temperatures 

into  absolute  temperatures,  §5,  p!7. 
for  finding  density  of  any  gas,  §5,  p46. 
for  finding  number  of  B.  T.  U.  required  to 
raise  temperature  of  body  a  given  number 
of  degrees,  §5,  p20. 
for  writing  chemical  equations,  §5,  p47. 


Rules  for  finding  specific  gravity  of  any  sub- 
stance, §5,  p2. 

for  finding  the  weight  of  a  body  when  its 
volume  is  known,  §5,  p3. 


Safety-lamp  details,  §6,  p52. 

lamp  houses,  §6,  p73. 

lamp,  Principle  of,  §6,  p35. 

lamps,  Locks  for,  §6,  p52. 

lamps,  Oils  for,  §6,  p57. 

lamps,  Relative  illuminating  power  of,  §6, 
P61. 

lamps,  Types  of,  §6,  p36. 
Sampling  coal  for  analysis,  §16,  p92. 
Sawdust,  §16,  plO. 
Scales,  Thermometer,  §5,  p!4. 
Scaling,  §14,  p7. 
Schiele  fan,  §15,  p24. 
Sea  coal,  §16,  p!8. 
Sealing  off  with  culm,  §5,  p67. 

off  with  stoppings,   §5,  p66. 
Seams,  Ventilation  of  a  long-wall  mine  in  flat, 
§14.  p31. 

Ventilation  of  inclined,  §14,  p32. 

Ventilation  of  slope  or  shaft  mines  in  flat, 

§14,  p28. 
Seasons,  Influence  of,  on  mine  ventilation,  §14, 

P45. 

Secondary  blades  of  fans,  §15,  p39. 
Self-filling  buckets,  §16,  p98. 
Self-lighting  device  of  safety  lamp,  §6,  p49. 
Selling  coal  by  analysis,  §16,  p30. 
Sensible  heat,  §5,  p!9. 
Shaft,  Air,  §13,  p2. 

Downcast,  §13,  p2. 

mines  in  flat  seams,  Ventilation  of,  §14,  p28. 

Upcast,  §13,  p2. 

Ventilation  of  a,  during  sinking,  §14,  p49. 
Shaw  gas-testing  machine,  §6,  p71. 

machine,  Testing  for  gas  by  the,  §6,  p72. 
Short -flaming  coals,  §16,  p!5. 
Shovel  bucket,  §16,  plOO. 
Shutter,  Fan,  §15,  p!3. 
Side-hill  storage,  §16,  pi 22. 
Sight  indicator,  Beard-Mackie,  §6,  p68. 
Similar  ainvays,  §13,  p!3. 
Sinking,  Ventilation  of  a  shaft  during,   §14, 

p49. 

Sirocco  fan,  §15,  p27. 
Slope  or  shaft  mines,  Ventilation  of,  in  flat 

seams,  §14,  p28. 
Solid  fuels,  §16,  p8. 
Solids,  §5,  pi  2. 
Sources  of  heat,  §5,  p!3. 
Special  lamps,  §6,  p47. 


INDEX 


xix 


Specific  gravity,  §5,  p2. 

gravity  and  density  of  gases,  §5,  p52. 

gravity,  Determining,  §5,  p6. 

gravity,   Determining,  by  hydrometer,  §5, 

P9. 

gravity  of  gases,  Determining  the,  §5,  pll. 
gravity  of  liquids,  Determining,  by  balance, 

§5,  P8. 
gravity  of  solids,  Determination   of,  by  a 

balance,  §5,  p6. 

gravity  of  solids,  Determination  of,  by  a 
specific-gravity  bottle  and  balance,  §5, 
P7. 

gravity  of  various  gases,  Table  of,  §5,  p5. 
gravity  of  various  solids  and  liquids,  Table 

of,  §5,  p4. 

gravity,  Rules  for  finding,  §5,  p2. 
Specific  heat,  §5,  p!9. 
Split,  Designation  of,  §14,  p8. 
Main,  §14,  p9. 
of  first  degree,  §14,  p9. 
of  second  degree,  §14,  p9. 
of  third  degree,  §14.  p9. 
Primary,  §14,  p9. 
Secondary,  §14,  p9. 
Tertiary,  §14,  p9. 
Splits,  Air,  §14,  p8. 
Equal,  §14,  p9. 
Free  or  open,  §14,  p9. 
Splitting  air-currents,  §14,  pi. 
air,  Limit  of,  §14,  p7. 
Calculations  in,  §14,  plO. 
natural,  Calculations  in,  §14,  plO. 
natural,  Pressure  and  power  required  when 

splits  are  equal,  §14,  p!4. 
natural,  Pressure  and  power  required  when 

splits  are  unequal,  §14,  p!5. 
natural,  Total  mine  pressure  and  power  re- 
quired in,  §14,  p!8. 
Proportionate,  §14,  p20. 
the  air,  Advantages  of,  §14,  p7. 
the  air,  Effect  of,  §14,  p2. 
the  air,  Requirements  of  law  in  regard  to, 

§14,  P8. 

Spontaneous  combustion,  §5,  p58. 
ignition  of  coal,  §16,  p32. 
ignition,  Precautions  in  storing  bituminous 

coal  to  prevent,  §16,  p35. 
Stack,    Effect    of   ventilating    furnace,    §14, 

P60. 
Steam  coals,  §16,  p!6. 

coals,  Relative  practical  values  of,  §16,  p26. 
jet,  §15,  p3. 

Stevenson  lamp,  §6,  p41. 
Stinkdamp,  §6,  p4. 
Stokes  lamp,  §6,  p51. 
Stopping,  §13,  p3. 


Stoppings,  §13,  p6. 

Sealing  off  with,  §5,  p66. 
Storage,    Bridge    tramway    system    of,    §16, 
p!24. 

Coal,  §16,  p!21. 

Dodge  revolving  system  of,  §16,  p!29. 

Dodge  system  of  coal,  §16,  p!26. 

Side-hill,  §16,  p!22. 

Trestle,  §16,  p!23. 
Storing  coal,  §16,  p97. 
Straw,  §16,  plO. 
Subscript,  §5,  p40. 
Sulphureted  hydrogen,  §6,  p4. 
Sulphur,  §16,  p2. 

Determination  of,  in  coal,  §16,  p94. 
Surface  expansion,  §5,  p25. 
Symbols,  §5,  p38. 
Systems  of  ventilation,  §13,  p!5. 


Table  giving  analyses  and  heating  values  of 
various  gases,  §16,  p53. 

giving  analyses  of  coke,  §16,  p40. 

giving  analyses  of  natural,  producer,  and 
coke-oven  gases,  §16,  p55. 

giving  analyses  of  petroleums  by  fractional 
distillation,  §16,  p45. 

giving  analyses  of  typical  American  gas 
coals,  §16,  p62. 

giving  approximate  heating  value  of  coals. 
§16,  p24. 

giving  average  values  of  K  as  determined 
for  different  coals  by  Lord  and  Haas,  §16, 
p86. 

giving  capacity  of  Dodge  bituminous  coal- 
storage  piles,  §16,  p!29. 

giving  changes  in  chemical  composition 
from  wood  to  anthracite,  §16,  p!3. 

giving  chemical  reactions  and  weights  of 
oxygen  involved  in  a  combustion  of  hy- 
drogen, carbon,  and  sulphur,  §16,  p76. 

giving  classifications  of  coals  as  determined 
by  percentages  of  fixed  carbon,  §16,  pi 4. 

giving  composition  and  calorific  values  of 
different  varieties  of  wood,  §16,  p9. 

giving    composition    of   extinctive    atmos- 

.  pheres  formed  by  a  mixture  of  carbon 
dioxide  and  nitrogen,  §6,  p!7. 

giving  compositions  of  petroleum  from  dif- 
ferent localities.  §16,  p44. 

giving  elevations  of  temperature  when  burn- 
ing carbon  in  various  quantities  of  air, 
§16,  p81. 

giving  formulas  and  number  of  atoms  in  a 
molecule  of  various  compounds,  §5,  p43. 

giving  heating  value  of  different  coals,  §16, 


XX 


INDEX 


Table — (Continued) 

giving  heating  values,  of  several  constitu- 
ents of  a  mixed  fuel  gas,  §16,  p56. 

giving  height  of  flame  caps,  iot  lamps  burn- 
ing various  fuels,  in  atmospheres  contain- 
ing different  percentages  of  gas,  §6,  p05. 

giving  horizontal  pressure  exerted  by 
anthracite  against  vertical  retaining 
walls,  §16,  p!31. 

giving  horizontal  pressure  exerted  by  bitu- 
minous coal  against  vertical  re"taining 
walls,  §16,  p!32. 

giving  proximate  analysis  and  heating 
values  of  American  coals,  §16,  p20. 

giving  proximate  analyses  of  anthracite  of 
various  sizes,  §16,  p!9. 

giving  proximate  analyses  of  some  Ameri- 
can cannel  coals,  §16,  p!4. 

giving  relative  illuminating  power  of  vari- 
ous oils,  §6,  p60. 

giving  relative  illuminating  powers  of  safety 
lamps,  §6,  p61. 

giving  relative  practical  values  of  coals, 
assuming  different  efficiencies  of  boiler 
results  obtained  from  three  coals  under 
the  same  boiler,  §16,  p29. 

giving  temperatures  of  ignition  of  charcoal 
prepared  at  various  temperatures,  §16, 
p79. 

giving  temperatures  of  ignition  of  various 
fuels,  §16,  p78. 

giving  temperatures  of  ignition  of  various 
gases,  §6,  pi  2. 

giving  theoretical  relative  heating  values  of 
petroleum  and  coal,  §16,  p42. 

giving  weights  of  air,  water  vapor,  and 
saturated  mixtures  of  air  and  water 
vapor,  §16,  p75. 

giving  ultimate  analyses  of  anthracite  and 
bituminous  coal,  §16,  p22. 

giving  ultimate  analyses  of  some  foreign 
cannel  coals,  §16,  pi 5. 

giving  weight  and  volume  of  various  gases, 
§16.  P73. 

giving  weight  of  coal  equivalent  to  1  cord  of 
different  woods,  §16,  p9. 

of  approximate  atomic  weights,  §5,  p40.- 

of  coefficients  of  expansion,  §5,  p26. 

of  coefficients  of  friction,  §13,  p20. 

of  composition  of  atmosphere,  §5,  p51. 

of  composition  of  fatal  atmospheres,  §6,  p!7. 

of  densities  and  specific  gravities  of  various 
gases,  §5,  p53. 

of  densities  of  mine  gases,  §5,  p47. 

of  diffusion  of  gases,  §5,  p61. 

of  elements,  symbols,  and  atomic  weights, 
§5,  p39. 


Table— (Continued) 

of  explosive  limits  of  gases,  §6,  p!6. 

of  explosive  ranges  of  firedamp,  §6,  p8. 

of  extinctive  atmospheres,  §6,  p!9. 

of  heating  values  of  various  substances,  §5, 
P56. 

of  mine  gases,  §6,  pi. 

of  molecular  weights  of  various  gases,  §5, 
P44. 

of  relative  velocities  of  transpiration  of 
various  gases,  §5,  p62. 

of  specific  gravity  of  various  gases,  §5,  p5. 

of  specific  gravity  of  various  solids  and 
liquids,  §5,  p4. 

of  specific  heats  of  mine  gases  and  vapors, 
§5,  p22. 

of  specific  heats  of  some  of  the  most  com- 
mon substances,  §5,  p21. 

showing  comparative  rubbing  surfaces  of 
airways  of  various  shapes  and  sizes,  §13, 
P12. 

Tan  bark,  Wet,  §16,  plO. 
Tapered  fan  blades,  §15,  p41. 
Temperature,  §5,  p!3. 

Absolute,  §5,  p!7. 

Actual,  lower  than  theoretical,  §16,  p83. 

and  pressure  of  gases,  §5,  p35. 

and  volume  of  gases,  §5,  p27. 

Effect  of,  on  firedamp,  §6,  p9. 

Measurement  of,  §5,  p!3. 

of  afire,  §16,  p79. 

of  air  in  furnace  ventilation,  §14,  p55. 

of  flame  of  blasting  powder,  §6,  p!3. 

of  flame  of  burning  gas,  §6,  p!3. 

of  ignition,  §16,  p78. 

of  ignition  of  gases,  §6,  p!2. 

of  the  fire,  maximum  theoretical,  due  to 
burning  oxygen  and  dry  air,  §16,  p80. 

of  the  fire,  the  fuel  containing  hydrogen  and 
water,  §16,  p82. 

of  air  columns,  Average,  §14,  p44. 
Testing  for  gas,  §6,  p62. 

for  gas  by  the  Shaw  machine,  §6,  p72. 

for  gas,  Lamps  for,  §6,  p37. 

for  gas  with  Davy  lamp,  §6,  p62. 

for  gases  in  the  mines,  §6,  p35. 
Test,  Valuing  coals  by,  §16,  p28. 
Thermometer  scales,  §5,  p!4. 

The,  §5,  p!4. 

Tin-can  Davy  lamp,  §6,  p39. 
Total  heat,  §5,  p24. 

Transmission  of  flame  of  initial  explosion,  §6, 
p26. 

of  heat,  §5,  p!3. 
Transpiration,  Effect  of  rate  of,  §5,  p63. 

of  gases  from  coal,  §5,  p62. 
Transposition  of  formulas,  §13,  p36. 


INDEX 


xxi 


Trestle  storage,  §16,  p!23. 

Tripper  for  belt  conveyer,  §16,  p!07. 

Trompe,  §15,  pi. 

Turf,  §16,  p!2. 

Types  of  centrifugal  fans,  §15,  p21. 

of  explosions,  §6,  p22. 

of  safety  lamps,  §6,  p36. 

U 

Ultimate  analysis,  §16,  pp4,  96. 

analysis  of  coal,  §16,  p96. 
Undercasts,  §13,  p7. 
Unit  of  resistance,  Value  of,  §13,  p!9. 

of  ventilating  pressure,  Calculation  of.  §13, 

P22. 

Units,  Heat,  §5,  p!8. 
Upcast  shaft,  §13,  p2. 


Vacuum  gauge,  §5,  p32. 

Partial,  §5,  p31. 

The,  §5,  P31. 

system  of  ventilation,  §13,  p!5. 
Vajen-Bader  helmet,  §6,  p32. 
Valuations  of  coals  as  fuel,  §16,  p23. 
Value  of  an  airway,  §13,  p!8. 
Vegetable  oils  for  safety  lamps,  §6,  p57. 
Velocity  of  air-current,  §13,  p!7. 

of  air  in  an  airway,  To  measure  the,  §13,  p25. 

or  quantity  of  air,  Relation  of,  to  power, 

§13,  P55. 
Ventilating  fans,  §15,  p3. 

furnace,  Area  of  fire-grate  surface  in  a,  §14, 
P58. 

furnace,  Coal  burned  per  hour  in,  §14,  p57. 

furnace  stack,  Effect  of,  §14,  p60. 

mines.  Means  for,  §14,  p37. 

pressure,  §13,  p!4. 

pressure,  Calculation  of  unit  of,  §13,  p22. 

pressure,  To  measure  the,  §13,  p31. 
Ventilation,  Artificial,  §13,  p!4. 

Blowing  system  of,  §13,  p!5. 

Calculations  in,  §13,  p34. 

Elementary  formulas  of,  §13,  p35. 

Exhaust  system  of,  §13,  p!5. 

Furnace,  §14,  p50. 

furnace,  Temperature  of  air  in,  §14,  p55. 

General  principles  of,  §13,  pi 6. 

General  principles  of  mine,  §13,  pi. 

Influence  of  seasons  on  mine,  §14,  p45. 

Mechanical,  §15,  pi. 

Natural,  §13,  p!4;  §14,  p37. 

of  adrift  mine,  §14,  p26. 

of  a  long- wall  mine  in  flat  seam,  §14,  p31. 

of  a  mine,  §14,p24. 

of  a  shaft  during  sinking,  §14,  p49. 

of  different  types  of  mines,  §14,  p26 

of  gaseous  mines,  §14,  p35. 


Ventilation — (Continued) 

of  inclined  seams,  §14,  p32. 

of  slope  or  shaft  mines  in  flat  seams,  §14 
P28. 

Plenum  system  of,  §13,  p!5. 

Practical  problems  of,  §13,  p39. 

Special,  calculation,  §13,  p49. 

Systems  of,  §13,  p!5. 

Vacuum  system  of,  §13,  p!5. 
Volatile  combustible  matter,  §16,  p7. 

combustible  matter,  Determination  of,  in 

coal,  §16,  p93. 
Volume  and  pressure  of  gases,  §5,  p34. 

and  temperature  of  gases,  §5,  p27. 

Mass  and,  §5,  pi. 

of  gases,  §5,  p27. 

of  gases,  Change  of,  due  to  chemical  changes, 
§5,  P49. 

of  the  gas,  Calculation  of  the  change  of,  §5, 
p49. 

temperature, and  pressure  of  gases,  §5,  p34. 

W 

Waddle  fan,  §15,  p23. 
Water  gas,  §16,  p63. 

gas,  Blue,  §16,  p63. 

gas,  Composition  of  purified,  §16,  p64. 

gas.  Impurities  in,  §16,  p64. 

gas,  Uncarbureted,  §16,  p63. 

gauge,  §13,  p31. 

gauge,  Calculation  of,  §13,  p33. 

gauge  due  to  the  action  of  fans,  Calculation 

of,  §15,  p42. 

Waterfall,  or  trompe,  §15,  pi. 
Weathering  of  coal,  §16,  p31. 
Weight,  §5,  p2. 

Atomic,  §5,  p38. 

of  one  cubic  foot  of  air,  §5,  p51. 

Molecular,  §5,  p43. 
Whitedamp,  §6,  p2. 
Wick  picker,  §6,  p56. 

tubes,  §6,  p56. 
Wicks,  Lamp,  §6,  p56. 
Wolf  safety  lamp,  §6,  p48. 
Wood,  §16,  p8. 

Burning  of,  §16,  plO. 

Composition  of,  §16,  p8. 

Fuel  value  of,  §16,  p9. 
Work,  §13,  p22. 

of  centrifugal  force  of  fan,  §15,  p33. 

of  producing  an  air-current,  Calculation  of 

§13,  p23. 

Wind  cowl,  §15.  p3. 
Workings,  Rise  and  dip,  §14,  p48. 
Writing  chemical  equations,  §5,  p47. 

Z 
Zero,  Absolute,  §5,  p!7. 


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